That's a great photo , I was told there not reef safe , do you ever see it bother soft coral ? (i mean reef safe within reason for a crab that is , most will eat anything if hungry enough)
The last one I had was eating my clown fish . Not sure if he caught it or found it dead. Yes he did clear out some unwanted visitors as well. And easy to catch and remove. If they go hungry your clean up crew is on the dinner plate.