the good,
love the fact there is no timer. the humor is just right. love the implication that over time the adventurers keep coming back for the transformations.
the only criticism
is the bra of holding in not fun as is.
have the curse checker or something we get to use every time like the enemy scroll tell us what enchantments they have.
a dedicated enchantment/special effect checker would open up a lot of design space.
suggestions
a dummy of each class so you can see the potion effects without being penalized.
and have the potion not be as temporary as they think.
keeping a little bit each time, so over time say every 5 to 7 days the adventurers relevant features are slightly but noticeably bigger.