We have been selling a good number of the Cheely E2 grip in stell and aluminum. Steel adds the weight and texture, while aluminum adds the texture, it may be a bit heavier.
I have now put 3 on various 2011's for friends. So far they have fit right onto every STI frame we have worked with. The only part that needs fitting is the beavertail around the tangs on the back of the frame. Technically you could go without fitting this, but I wouldn't.
They have a great feeling to them, and the weight is pretty nice since it is right where you typically want it.