I've tried them. They do eat aptasia, but they are expensive and undependable for a typical reef tank, IMO. They may or may not reproduce (or even survive predation) and they may or may not be able to eat the aptasia faster than it grows. And if they are successful, they will die because they don't eat anything else. Invariably you'll have one or two aptasia survive them and they cycle starts again.
I've had good luck with peppermints in a dedicated tank--one rock at a time sort of thing.
If you really want to experiment with berghia, check out berghia.net. That's where I got mine. Larry O. is a fine breeder.
