They are great until they don't have parasites to eat and become predators of opportunity. I have three and they are carinvores as they have eaten one of my three mini rock lobsters on my christmas tree rock, devastated my pod population, and have even been seen eating a bristle worm or two. I am not fully convinced that they have not eaten a pepermint shrimp or two.
I do think that they are really cool and are definitely afraid of NOTHING as mine fight over who gets to jump on my hand everyone needs to be mindful that they are opportunistic.
Just my .02 worth.
Earl