I bought a couple of the Mec-Gar 15 round magazines (CZCOMP15AFC). They fit fine, with some interesting differences compared to the factory CZ magazine that came with a P-01 Omega. The following is mostly for other CZ newbies like me who are looking for extra mags:
The magazine body is about 3/16 inch (~4mm longer), The plastic base plate wraps around the end of the magazine to fill most of the gap between the end of the mag and the grip. The oem mag is a closer fit, if it matters. With either one, about half of my pinkie (I wear size L gloves) rests against the base plate.
The follower is different (and blue), and the spring is shorter, and made out of a thicker wire.
The base plates and locks are different on the two magazines, but they both look ok. I assume the soft rubber base plate was designed to go with the rubber grips, and it is a better (closer) fit overall.
The Mec-Gar magazine is labeled "Anti-Friction Coated" on the package. Not sure what that means. I wiped it inside and out with some light oil, because it seemed pretty dry and it won't hurt to err on the safe side.
I'd rather have the oem magazines if the price was closer, but the Mec-Gar mags were $22.75ea plus shipping online at CenterFire Guns (and I'm cheap).
I do like the Mec-Gar magazine design better in one important aspect. The follower is designed to better protect the spring from being overcompressed against the base plate. In the long run that may be a more important feature than how it looks (for people like me who often can't count to 15, anyway).