They're pretty voracious eaters. I would definitely not consider them 100% reef-safe, however you could keep them with some inverts without an issue. They'll eat feather dusters, small fleshy polyps, and I would assume they'd pick at clams. He will also pick on any sick fish without haste.
I've got some anthellia, xenia, palythoas, and rics in there with him. He's not picking at them, currently.
Though they are EXTREMELY adorable and easy to love, do keep in mind their fragile health and large adult size.