I have a shadow vessel (urchin) in my tank and he cruises around with little to no muss or fuss. I have the spiny type and not the tuxedo. Generally I believe them to be quite helpful to a reef provided you DO NOT TRY TO PET THEM! :funny:
i got an urchin as a hitch hiker. found out later that it was a rock burrowing urchin. i was always amazed by the "grip" it had, and was never able to get it out until recently. i plan on taking it back to the lfs where i got the rock, and seeing if i can get store credit for it :funny:
urchins are also a little clumbsy. they can be bulldozers. i would not recommend them to anybody who has small frags they are trying to get encrusted onto the LR. the really pointy ones can tear up some LPS.
newfiemom-you can have anything you want in your tank.