I have one that is shaped identically, but is molded from black plastic. I ordered mine from Fulton Armory (the only thing I could afford from them [:)]).
I like mine, but the general consensus around here seems to be that dry-firing the AR does not damage it and things like this are a waste of money where it is regarded.
Possible firing pin/hammer damage aside, I like it mainly for the short stroke involved to recock the hammer, and that the dry-fire device also acts as a safety "lock" of sorts due to the fact that even if you load up the rifle and chamber a round, if you have this thing in the bolt carrier the rifle will not fire until you remove it. However, it does make for an amusing time at the range if you forget to take it out before attempting to fire......not that I have ever done this [noclue].
Is it worth it? I don't know. If I had found this page first, I probably wouldn't have bought one.