There have been a few incarnations of them. The newer ones, which I can pretty much tell yours is, uses one frame for all calibers. Back in the earlier days there was a small and large frame size. The small frame size was for 9mm and 40 S&W, and the larger frame for 45acp, 10mm, ect.
So when you order mags you want to make sure that you get the ones from the large/one size fits all frame. I had an earlier Witness 9mm with the small frame size in wonder finish. The one thing I did was to wolff springs in my mags and recoil spring. I shot hot 9mm loads so I put a little stiffer recoil spring.
They are basically a little upsized and simplified CZ75, which was called by the late Col. Cooper as the best 9mm combat handgun ever made.