I just bought one on eBay for my SA XD40 subcompact, works great, installed in 30 secs. The hole lined up perfect and now much easier to grip. I think I paid 8.50 or so. Well worth the money.
I have them on my LCP magazines and they make all the difference in the world. I also have a promag with extended grip and a factory Ruger extended grip but the pearce are the best by far.
I have the +0 extensions on both my Glock and my Kahr CM9 and I like them. I don't think I would add any extensions to the Kahr that add extra rounds, though. Kahr magazines tend to be problematic the way they are and I wouldn't want to make it worse.