I have both in my tank and have had zero issues. From my research both are "mostly" reef safe but you will run into the occasional individuals who cause problems. I love our emerald crab. It's freaking massive and waves it's claw around at me or any fish that get too close to it. Occasionally it will dig into corals, especially the polyps and I freaked out the first time I caught it doing that but it didn't damage anything. They'll clean up algae and left over food from around the coral and they're not exactly careful about it. But mine has yet to damage anything. The only member of our CUC who has damaged anything is the urchin who munched on an acan. Seems like that was a fluke because it only happened once and it's been a well behaved citizen ever since.