Pom pom or boxer crabs are, in my opinion, totally reef safe. They are very shy though and you will be lucky to catch a glimpse of it now and again. I have one and it has never bothered anything or been bothered by anything. The anemones they hold are tiny and they wont really go after ornamental invertabrates at all. I have seen mine mopping up bits from the sand and rocks and mysis when i feed the tank. They are very beutiful and interesting on the other hand, and watching them wave the anemones at the cleaner shrimp is very funny. I have kept it with a huge emerald crab, the pom pom is smaller that one of the emeralds claws but they had no problems.