By devils do you mean Red Devils? If so then I'd say no. A flowerhorn is no match for a red devil. They do have the ability to clear out tankmates though. Any fh I've owned was nasty, and needed to be divided. I think they know they are a man made hybrid and they hate the world because of it. They should be treated like any other large aggressive cichlid, though an expensive one. They have great personalities IMO, and they're great fish for people who enjoy hybrids, just not my cup of tea.