I have had mine for about 6 months now. He has eliminated all of my bubble algae and cleans up any un-eaten food on the bottom of the tank. I have noticed him climbing on some of my soft corals every now and then but he has not caused any noticable problems. I have heard of others having problems with these guys eating corals and coraline algae though.
RD--It's kind of a gamble. The first one I had was fine for about 3 months, then started to go after a newly added torch coral. I removed him and went emerald-less for a while until the valonia got really bad. I tried another one, and this one has been fine for about 6 months. He has gotten huge and eliminated the tank of valonia. I later bought another one for a different tank and he is ok as well. So, you may have to try a couple of different ones, but it is definitely worth the effort. Good luck,
I bought one for valonia control. The only things I ever saw him eat were coralline algae and mushrooms. They seem to be one of those hit and miss type animals. Some people have good luck with them, some don't.