There will be no really significant consequence for using the tadpole and the game will end effectively if not exactly the same for those that do and do not. The "correct" way to play the game will be to, at a minimum, have a companion use the tadpole so everyone gets the super powers(bonus points if you use a companion you don't ultimately want endgame so if they are "lost" after Act 1 no big deal).
The shallowest game play all round will be a custom MC who never uses the tadpole(or forces a companion to do so).
