My thumb rest slide lock lever came in yesterday and I installed it last night.
I would love to show you what it looks like but I can't seem to figure out how to post pictures on this site.
I will try to find out how to and maybe do so after I get to try it out.
So far, I like the feel of it, but until I can put a few hundred round though my S2 with this installed, I will hold off on any more comments.