Why or why not would an European Polecat be good for a zoo?
The European Polecat would be good for a zoo because, like the ferrets they so closely resemble, they'd be lively, active creatures. They would be a good choice for a children's zoo, where the focus is on animals that are fun to watch and not threatening (to the eye—I'm not discounting the polecat's potential to bite.)
As far as why they wouldn't be good choices, well, to be frank, they look a lot like ferrets, and may therefore seem too common. They also would be likely to escape if given half a chance.
The European Polecat would be good for the zoo, because it is sociable and friendly, so it is a good exhibit for usage in an education trip for the students. As they are adorable, more children would want to get up close and personal and take some photographs to keep as souvenirs.
It won't be good for the zoo because it is not very vocal in speech, and would give sudden spurts of high screeching, so may scare some kids away.