I had one, until someone fell on it (crab or snail) and pretty much killed it.
Only suggestion in picking one I've got is try to pick one that's moderately expanded and isn't all retracted at the fish store. It's hard to know what you're looking at when you're looking at one for the first time, but here's a healthy one...
This is a short tentacled one, and it's fairly "puffed up" in this shot.
Keep them on the sand bed and not on your rocks because they'll move. Really... they will. And learn from my mistake and don't put it under an overhang or shelf on your live rock where some clumsy snail/crab might pitch off and land on it. They don't like that as they're quite delicate. They're hardy... but delicate.