Good Or Bad Urchin?

[whatcaneyedo]

I have a rock boring urchin (Echinometra lu****er) in my frag system with... lets just say 40 different species of coral because I don't feel like counting. I've had it for probably three years now and the only problem it's given me is that it will eat at the silicone seam on a glass aquarium. Which is why its in my frag trough. In all of this time its never actually tried boring a hole in any of my rock or coral. Without any silicone it seems to be quite contempt to eat coraline algae all day and leave everything else alone.