They perch on corals and then dart out to snag food just like a hawkfish. It might irritate some corals but it has not been a problem IME.
Downsides are that they can envenomate you and that they are probably hard to find. They shouldn't be more than $30-40 retail though. They can of course eat small fish and shrimp but we're talking really small. I wouldn't keep it with small gobies but it should be fine with clowns, dottybacks, anthias, etc.