I'm interested also, I only had the pencil urchins and they were horrible on my coraline (that's an understatement).... I'd love to find one that stays on the sand, or at least leaves the coraline alone....so I'm gonna follow this post. Sorry I couldn't help more, but you can cross those ones off the list at least.
Hopefully Bang will chime in, I never heard of that type, and give some info.