I have a couple that are now getting to be about 3 inches across. First time I ever had them grow so large. They haven't bothered a thing. When I feed, they come tearing out from wherever they are hiding and grab for the food. But to this point, they haven't bothered the peppermint shrimp, coral banded shrimp, or anything else.
I watched two of them yesterday wrestling for food, but they didn't even seem to be violent with each other. I'm not sure if it's true, but I read somewhere that with their claws shaped as they are (sort of rounded), that they aren't supposed to bother anything.
All I know is as long as I have emerald crabs, I have no bubble algae.