Most Thalassoma wrasses (including T.lunare) are technically reef-safe in that they don't consume Cnidarians (corals and such). However, they wreck planktonic populations and some may eat smaller clams (including Tridacnas). They're one of many wrasse genera that dig up the sand; if you plan on keeping a healthy sandbed, this wrasse is not the way to go. Most get quite large (6-12 inches) and some are very aggressive bullies. Lunares get to about 10 inches and are moderately aggressive.
I have a lunare wrasse in a 120 gal FOWLR with a DSB. Yep, it looks like the wrasse scoops up sand and spits it out occasionally. I believe it ate the few snails I put in there. It showed interest in a couple of large hermits I put in, but both are still alive after several months. I have sea urchins for algae control. The wrasse hasn't bothered them. I have a frag or two of mushrooms and polyps, it doesn't bother them except by knocking them over. The other tankmates are a yellow and regal tang and a blue devil damsel. The damsel keeps a good eye on where the wrasse is, but the tangs do fine with it.
