Tahm Kench has received a number of buffs to the point that people like Voyboy have been monkeying around with him in the Jungle. I've tried a couple of variations on builds for Tahm to see how he stacks up.

No. 1 Issue

I haven't tried out a build that gets you through more than about three jungle camps and slowly at that. Generally you will have to back after Krugs and Red Buff even with a good leash. This means that he is very vulnerable to counter juggling during the early stages of the game, by either being caught while on low health or simply being out of the jungle as you back to heal.

Now after you get a point in you three basic abilities, life gets much easier.

I've tried maxing both Devour and Tongue Lash and it doesn't seem to make that much difference in terms of clear speed.

Part of the issue is that he can't eat the Red Brambleback or the Blue Sentinel. This makes those camps interminably long to take down. I've tried starting those camps so I can get help from my laners and it doesn't seem to make that much difference.

Once you do get going though you have a choice of going complete tank or more bruiserish.

I find going Enchantment: Devourer to be more entertaining. You can pair that with a Titanic Hydra and Dead Man's Plate for some insane damage output.

You can round out your build with something like Spirit Visage and Warmog's Armor for some insane tankiness plus even more damage output because of the passive damage you gain by putting levels into Devour. Boots are case by case. My top three choices would be Boots of Swiftness, Mercury's Treads, or Ninja Tabi.

Tahm is super good at peeling, so if one of your carries is fed, all you do is stick by them and fend off any attackers. Word of caution though, try not to deposit a half health ulting Nasus next to your carries.

Late game with the above build you may even be one of the carries, albeit a really hard to kill carry.

Devour

If you eat say an ulting Garen before the animation completes, it will stop the ult.

Oh since you don't have any preconditions to eating an ally, unlike an enemy on which you need to get three stacks of An Acquired Taste it is easy to accidetally eat a nearby ally close to your target rather than your target, so be very careful where you click when attempting to devour someone in a scrum.

Devour

Is kind of hard to use for transportation if you aren't in a call with one or more of you laners.

Also I've had trouble with accidentally only hopping a short distance if I have it on smart cast. It has two components. You first have to select a target location and then press R again to go there otherwise you will sit there and channel for the full duration even though there may be no one there to hop aboard.

If you want to go directly into the Dragon pit {from blue side) you have to be about even with the first line of trees outside your base.

tldr;

If you make it out of the early game and you laners are in decent shape, you are probably going to be able to carry the game if you go Devourer. If you get invaded and your laners get shut down you are going to have a difficult time coming back.

Update

Running 9-21-0 with Atk Spd, Health/lvl, MR/lvl, Arm Quints you can get though the majority of the jungle in pretty good order if you go Devour then Thick Skin, but it is clean your shorts out close on Red. You heal up a pretty good amount after. Bad time to be caught by the other jungler though. Double juggling could fix this, but not something I would count on at my ELO. I would get Tongue Lash third to have an additional damage ability, then one more in Devour if I am going to farm though, if I were going to gank, I would opt for my fourth point to be in Tongue Lash for the increased damage and slow.

So farm:
W+E+Q+W

gank:
W+E+Q+Q