The prince nymph is one of the most versatile flies in existence. It catches everything from trout and salmon to panfish and carp. It doesn't look like any one insect in particular but it does look like the kind of thing that fish eat. It has been a top performing fly for years. Just ask any fly fishing guide.
The flashback prince has a bit of flash material on the wing case that reflects and shines just enough to bring in more bites.