I don't think they are very aggressive when you put it in terms of potency of sting. I think the problem some have with them is they may spread like wildfire and overgrow other corals and that's the way they kill them.
The nice thing about them is if you can peel up a piece of the mat and peel it right off the rock.
Well I took everyones advice and sold all the LR that had GSP on it to the LFS, in turn I got 2 awesome huge rocks (center and right pieces) , a tube anenome, and 2 sps (digy and a tort)... Check out the new aquascaping and corals....