Their are consequences for using the tadpole. Pretty dire ones datamined so far. An item you get in the underdark heavily implies what one consequence is.
Ncps can control your mc. Probably worse than ethels masks forcing a wisdom save or lose the turn every turn. The mindflayer in the underdark strengthens your tadpole but gives you a item to resist control. I'm pretty sure he lied about wanting to remove the tadpole and really secretly wanted to strengthen it for unknown reasons. It knew what it was doing in my opinion.
