I have one in a 29 gallon. It eats any and all crabs, and most snails. I've got one in with damselfish at the moment, and everybody's kind of happy. Will eat feather dusters. Will eat brittle stars. Will also eat large shrimp, squid, blackworms, and mysis. Kind of eats algae, but not really....
If you get one, get a large protein skimmer. I've got a Coralife 65 super skimmer, and it barely keeps up with the puffer.