Interesting, I tried Tigerheart on Karlach during Act 2, and I was very disappointed. The aoe damage is meagre and has only a very small area. Maybe I did something wrong. On many NPCs you cannot apply poison or let them bleed, so it's quite situational. If you can do it, I find the effects of the aspect of the last animal on the list (don't know the English name), maiming, much more interesting than the relatively small damage increase of the Tiger aspect.
In the end, I changed her back to Berserker (Barbarian 9/Rogue 3) with emphasis on throwing, it's a lazy approach, I know, but so nice and easy.
