I would say not very rare. When I was looking for a 156 or M1, I tried the B&R dealer in London, and they said they could get hold of a couple of new M2's if I was interested in having one. That was about 6 months ago. At the end of the day it's a Valjoux movement, exactly the same as the 256. I suppose you could say "rare" in that B&R and Sinn do not have a working relationship, but certainly my experience was that the dealer could get hold of one.What are the differences (if any) between these two watches? I know that Sinn manufactured these for B&R, and from photos I've noticed the different hands, but are there any others? How rare, or sought after, is the M2?