Some years ago when I was shooting a lot of IDPA, I bought some OEM mags for the CZ from CDNN. When they arrived I saw that the package was marked as CZ original equipment, but the back of the same package card showed that the mags had been made by Pro-Mag. They were, in every respect, identical to the CZ factory mags and gave, over a period of years, the same service.
CDNN is generally pretty reasonable about returns if the product doesn't work as indicated. I'd risk buying a couple if I needed some mags. (Unless, of course, I could find some Mec-Gar mags for a few dollars more.) The problem with CDNN shipping costs is that they are high, and you need to buy several of whatever you buy to not pay too much per unit purchased.