I've been doing tests on which junglers can actually get Feral Flare at pre 30 time, keep it, and make more use of it then the spirit items. The tiering will be explained after this paragraph, the purpose is mainly to see the overall balance of Feral Flare, in relation to champions. If it turns out to be Broken on a majority. Then we can conclude maybe the item itself is broken. You can comment on your own experiences as well.
Update #1: After Nocturne, I am actually worried. There shouldn't even be 2 God Tiers. But this item is providing an abonormal amount of Baron Solo's within the 20-30 minute mark, considering the average time it takes to GET THE ITEM is around when Baron first spawns. This is coincidental but leads up to obvious plays. The item is absurd on some champs, and still outright good overall. Whether or not they have a decent clear doesn't matter, once they get Madred's their clear time sparks up, Wriggle's only boosts it more. The item is too good.
Update #2: This is just getting ridiculous. Very ridiculous.
Update #3: Testing is not even finished, yet we have Feral Flare nerfs on PBE already, from 25 to 30 large monsters. This adds probsbly around 2 extra minutes to farming required. This does change Tiering when the nerfs hit servers. Seems the item was infact, a bit too good.
Note: These tests were mostly done with 9/21/0 Masteries (I literally called them jungler, you can check my lolking for the specifics) with the exception of Kayle, Teemo, Skarner, and Hecarim, who used 21/9/0 (Hybrid Jungler), Rengar, Quinn, Sion, Gangplank, and Kha'Zix 1515/0 (Rengar/Kha'Zix), and Nautilus 15/14/1 (Nautilus). AS Marks, Armor Seals, MR per level Gylphs, and MS Quints, with the exception of Sion, who had full Health runes. All tests are done under Medium to Best case Farming Scenario.
G(od)-Tier (Just broken)
Shyvana: 15 Minutes. Jesus Christ she's broken again. I have 0 losses with this witch.
Aatrox: Why'd I bother testing this one. As figured the heal and magic damage is broken on this guy when combined with his W. it can be farmed to the point he always outheals his damage toggle. He got it at 12 minutes. Twelve Minutes. This was also my first Aatrox jungle game ever. I went 4/0.
Kha'Zix: 15 Minutes. I was surprised. You thought he could snowball before, once he gets this his snowballing only escalates. It's passive not only bypasses peopel who try to build against Kha, it also heals for people who build against him. His clears also become phenomenal. Stacks well with his Passive.
Nocturne: 15 Minutes. No reason not to get this, as expected its his perfect jungle item. Acts as a far cheaper bork. I solo'd baron with only it as sustain.
Trundle: 16 Minutes. Oh boy, the sheer stacking of increased healing. Between spirit, his W, and the mastery, Feral Flare gives him almost 60% the mileage (maybe more, forgot exact numbers) And works well with his entire kit. It acts as a cheaper BoRK, which allows him to get tankier quicker.And if he's ahead enough he can buy BoRK to combien with Feral Flare.
Teemo: 16 Minutes. Rush Flare, Rush Runaan's. You're heal is now trippled, get max attack speed. Proceed to do more damage then AP Teemo ever could. I fought a LeBlanc, she died before she could even do her second spell. It wasn't even fun after a point. Jungle Teemo seems to be far better at the moment.
Sion: Although initially blue dependant and slow. Letting him farm is a cardinal sin if he has flare. Once he ults if he's tanky enough he's not going down, I solo'd a Baron, while the entire enemy team were trying they're absolute hardest to stop me, and then I proceeded to 2 shot they're aatrox and and go back to baron, then killed their gragas who tried to ult bodyslam in. He's a badly modeled giant ball of fuckery far faster then top sion. Atma's gave 57 ad with only Trinity as my only health item. at the 30 minute mark. Sion also benefits from Wriggle's gold, combo' with avarice. In the same manner of Gangplank, however, Sion doesn't need to build health. And the more he arms, teh more ad Atmas Gives, the more magic damage and heal Flare gives, and the more health he has. His hits feel Nasus-Esque.
Udyr (Tiger): 18 Minutes. So far, he can solo baron as full tank with it. Pretty good.
Udyr (Phoenix): 17 Minutes. The speed helps with Phoenix, although he doesn't hit as fast since Tiger is not maxed. He has amazing clearing for farming it.
Master Yi: He got by 15 minute mark. And continued clearing. Built normally but sold boots since shiv and tirnity were fast enough. (so I'd have room for a mog). Don't give this guy kills or assist if he gets flare (and he does, very early). Or he's just impossible, Even with Varus, Nasus, Ori, Thresh, and Zac, in my first try, went 15/8. Wriggle's anf Flare also boost he gold obtained from avarice when the unit killed is a jungle unit it appears.
Nautilus: 18 Minutes. It's basically a Wit's you buy first instead of last, his clear time becomes amazing and synergizes well with his W. He can still gank well and earn this within the 20 minute mark.
Vi: 16 Minutes. Very viable choice, and one that actually moves into late game. Not too far better then SotEL or SotAG. But cheaper, and gives a second ward. Allow her to dish damage with tankier builds so she's not a one trick pony. Her clear time is pretty good with it.
Rengar: 15 Minutes. Probably the only item he should take. Once he obtains it he has 2 snowball items, neither of which lose stacks.
Warwick: 15 Minutes. No real reason not to get this, synergizes so well with his W and Ult. He has no reason not to farm between ult ganks and pre-6.
Jax: 14 Minutes. Pubstomp the yard. I build alot of Lifesteal, Spell Vamp, and damage on him, this is just a fucking cherry the size of the icing and cake itself. Probably his best jungle item since even the bonus ward goes so well with him. I don't find him outright broken since his damage is high enough he can just get normal sustain. But this will help him against tanky targets.
Hecarim: 15 Minutes. He's no longer a one trick pony. It's actually very strong and synergizes with his W really well, getting a Trinity or Iceborn also goes very well, he can be a teamfighting sustain machine. I was 1 v 4'ing. However still has Mana Issues, though he doesn't require his spells to the same extent as before.
Skarner: 15 Minutes. As the only jungle item to give attack speed. Its also his best. It synergizes with his entire kit incredibly well, making his clear time phenomenal while making his Autoattacks hurt even more besides his sheen procs. Also has mana issues, but like Hecarim, doesn't really need his spells as much.
Gangplank: 16 Minutes. He takes blue, farms alot, his ganks suck, and his first clear isn't that fast. But by god, this is the epitome of Bankplank. He reaches Late Game 10 minutes before anyone else. and if anything, he can get Flare Early, continue farming fast, and by late game is in a far better Fighter Position then expected, once the Teamfights start he makes up for most of early game's nuances. Make some Bank.
Cho'Gath: 15 Minutes. The item itself goes well with his E, and increases clear time without needed spell spam. gives him a nice amount of sustained DPS similar to Wit's End, but provides sustain to boot.
Twitch: 16 Minutes. Similar to Teemo's situation, although initially rough, once enough atack speed is racked up and combined with a runaan's, he's a healing monster. Unlike Teemo however, his ult ist he crux of his synergy. However Twitch requires more skill to line up his shots.
Olaf: 14 Minutes. Short time, it goes well with his kit more then the spirit items. Not much to say on this.
Mordekaiser (AD): 17 Minutes. Karthus is probably the only Shadow Isles champ who can't use this. He can Sustain Tank like a Sion or Aatrox.
Nasus: 20 Minutes. It's nice on him, but it makes his farming focus last alot longer, makes getting the large monsters far more important then they were before. I told a different jungle nasus to get it and he carried the game for us, however if he can't farm then he still suffers Nasus problems.
Kayle: 18 Minutes. She does just fine in the jungle to farm, and can get it in a time frame that matches other farming junglers even as a ganking jungler. And once she obtains Feral Flare, she can become quite volatile to fight if built on hit (Nashor's, Wit's End). However, she is still a ganking jungler, and can helop the team out more by simply ganking, delaying time. Even more so, Why play jungle when you can simply go into a lane and do similar damage without leaving your team in the gutter.
Mundo: 18 Minutes. Goes well with his E, once he gets Flare it serve as a decent way top help against his costs. Not much else. He's not as tanky as quick though.
Lee Sin: 18 Minutes. Not bad, doesn't help with moves but gives him decent clearing and sustain in teamfights on top of Iron Will
Xin Zhao: 20 Minutes. He can snowball and do well with its heal comboed with his W. But he can snowball alot faster and sustain alot better just going toplane.
Darius: 16 Minutes. Probably makes his jungling actually fast and worth it. His mana costs are low enough he doesn't require a Spirit Item, combined his with his ganks being low maintenance, he can get it quick, and it helps make him unbuildable against in combination with Sunfire, as he deals just too much of a variety of damage. This was in a 4 v 5. Though our teammate later rejoined and was surprised we had a lead.
Quinn: 14 Minutes. Requires a hard leash. And before flare, relies on blue a bit. Howevr if she can begin carrying earlier then in bot or top lanes.
Evelynn: 16 Minutes. Goes well with he E attack speed boost, ravage does not proc it however like some people though.
Volibear: 15 Minutes. Was actually surprised by this one. Sadly when it comes to Volibear, people are prepared before hand knowing they have to deal with high sustain, thanks to his passive. So sadly it's far more likely for him to be Grievous Wounds'd.
Thresh: 16 minutes. Think about this, before flare, Thresh was one of the worst possible junglers available, slow clear, and can die from first clear. squishy, and has low level 1 armor making him easily counterjungled. Post Flare, after his first clear, he speeds up exponentially in every way, between souls, flare stacks, attack speed from madred's and wriggle's, and the armor from each camp. Similar to Nasus, but unlike Nasus he is meant to build attack speed if he is to be AD or built in any way offensively. Make sure you have a team that can handle until level 6, and is willing to do Thresh Jungle, or they will only make it impossible.
Tryndamere: 18 Minutes. He can get it alright, and early too, but doesn't stop tryndamere problems. Unlike Nasus however, he has no excuse to keep farming just for flare.
Jarvan IV: 16 Minutes. Does pretty good, has decent synergy with his E. But his armor reduction doesn't. If you build him tank, this is a decent option. But he still needs to gank to stay ahead.
Shen: 18 Minutes. Even with flare, his clear is actually still slow, and he scales better through ganking gold then overall farming. Although it's cheaper then wit's or bork, it takes awhile to pay off in comparison.
C-Tier (Can obtain before 20 minutes)
Shaco: He got it by 18, but as a gank heavy champ, I only did so by leaving my team angry at me. ( :( ). Not as worth as it could be, considering he gets crit items like Shiv or gets Hydra. Better to stay standard.
Zed: 17 Minutes. Look at what RoznosicielCiast said in the comments. Thanks for sharing
D-Tier (Can obtain before 30 minutes)
Not gonna bother Tier
Amumu, Rammus, Sejuani, Karthus, Gragas, Alistar, Garen (I've done this once, actually worked, weird), Maokai, Malphite, Nunu, Pantheon, Wukong, Zac
To be tested
I'll be filling this out more as I do more games later on. If there's any champs you want me to check out to see time taken to get the flare, and overall effectiveness let me know.