I run it and like it as a way to make the aggro decks act a little differently. Flutterfox is never going to be a premier threat, but it can do work if you're trying to weave artifact-based aggro themes into White. It's always card 20-22, but if you're got some artifact aggro or equipment hanging around it can be really annoying to deal with, and winds up eating removal more often than you'd expect. However, it being "better" than Mistral Charger is really going to depend on how many 1/1 flying tokens you have in your environment, so I'd first look at that to determine if it's even worth considering. Stone Haven Pilgrim is a good alternative, but frankly they work really well together and I've considered running both.