I'm fine with a evil parties getting a super powerful object in addition to the gloves, shield and amulet that are for evil parties. But the tadpole powers are not minor. Are you not developing your absolute powers? I don't think you say those powers are separate from evil playthrough. Give in, seek power and be rewarded.
I am evil. I want power and don't care who I have to step on to get it, but I am not suicidal. Power which will greatly accelerate the end of my life is power at too high a price. I'd be happy to seek power and be rewarded, if I am convinced that there is a reward for me.
Right now though, we've got a bunch of people who are denying the existence of tadpoles trying to tell us that this power is great. What would convince me are people who know about the tadpoles inside their own head and know a way to use them to continue to survive and thrive without being turned into a Mind Flayer. I do not find the arguments for power convincing coming from people ignorant of the source of their own power. That strikes me more as those people being suckers being used.
