We have five Barnacle Blennies right now and they are some of the coolest fish we've ever put in out tank! They each occupy their own barnacle hole and eat like little darts, whizzing in out and out so quickly you'll blink and miss it. They're great reef fish, and because they come with their own home (our LFSs always gave us the barnacle to take home with the blenny) they acclimate quickly and other fish don't mess with them.
I wouldn't hesitate to pick one up if you like crazy, lively little fish!