Will it have any effect?
or will it be like carbon, where the effect is negligible?
Echoing what others have said, it is definitely negligible, if there is even any effect at all.
I haven't adjusted my dosing after the addition of purigen and everything grows just as it did before I placed the purigen in my filters.
I actually like using purigen more than carbon as well, particularly for its ability to be recharged and the ability to presumably visually identify when it is spent and needs to be recharged.