I would be willing to bet there are going to be pretty serious consequences to using the tadpole. I would be willing to bet that after even 1 use, certain dialogue option will be removed permanently. Not sure what the effects of that will be...but if I am right who knows how many conversation branches have been sheered, how many potential side-quests lost, etc.
This is just an example of how I can see this having an effect later on in the game. If the main protagonists of the game really are the mind flayers, then in the fight against the mind flayers there may be certain guilds/groups/whatever looking to recruit but if you have any portion of the tadpole left over in your brain, you might not be trusted to join their group. It could be that one use of the tadpole ability during gameplay increased the CD by +2 or something, and maybe 4 or 5 uses makes you ineligible to that group or something. That would make sense to me. May not be in the game, obviously, but something along those lines is what I am imagining for consequences.
