That AT&T KB305 is really cool. I've seen a lot of Model Ms, and this is my favourite. The plate is pretty nice, about on par with a second-gen Model M but the barrel frame is made of a much harder material, changing the sound. The controller is very nice and the cable is detachable with actually useful cable channels. The feet are fully adjustable instead of the flip up/down feet of the IBM version. The cable (detachable) is a standard PS/2 to 4p4c, just like the dolch.
Downsides: case is a little bigger (I know) no KB shelf, and the feet aren't very "solid" feeling. Despite that, I like it the most.
They aren't rare like an industrial SSK but are quite uncommon (like a normal industrial). Excellent KB and I strongly recommend picking this up.