They are a pretty cool fish. They are a quite hardy fish, but they are somewhat reclusive, and more nocturnal by nature. Not a candidate for a Sohal Tang/Clown trigger/Mappa puffer type tank, do much better in a reef type tank. They can sometimes be a little finicky to get accepting prepare foods. Your inverts should be fine with the Comet, save for any small shrimp.
Oh and no, they are not related to groupers in any fashion.
You have PM on the way to a great article on Comets.