The CW line has had significant problems (word of mouth/youtube).
I have a MK40 and never had any issues with it. The CW line is the "economy" line and it seems Kahr left out quality control to save money. :-(
I have heard good things about the PM9 but heard some issues with the PM40 (maybe early models) where the extra recoil of the 40s&w caused the polymer rails to warp. I don't know if they resolved that issue or not. I decided to go with the stainless MK40 and like it. Hindsight I would prefer the K40.