Hmmm...I can't really agree with any of the above comments. I've had two in a reef tank for a few years, the only problem I have with them is that they can scare some corals into closing up when they climb on them, but its only temporary.
They don't bother the sand bed, as a matter of fact, they help keep it level and even. My sand bed is full of pods, worms, and all kinds of critters.
As far as crab "poop", I've never seen it, so I doubt its too much of an issue.
I love these guys, and unless you have a lot of SPS corals, I say go for it.
![](https://forums.saltwaterfish.com/image/noimage/true/width/525/height/525/flags/LL)