I never used the tadpole powers,so can't really comment on tha, but I thought, you become a half Illithid through using them?
I would like a bit more reactivity to my Durge though. I mean she is resisting and normally good, but then THAT scene happens and none of the companions have anything to say. When I told Gale afterwards about my urges, he said 'As long as you don't act on them, all is good' - with the body still lying there.