On the mag interchangability question: the Witness/Baby Eagle mags are a little wider at the front of the opening and are a little more squared off. I bought a couple of these a while back, thinking they would work in my CZ, and every one of them would lock the slide back with 1 round left in the mag. They also protruded from the bottom of the grip just a tad, but if you fully inserted them, they would, again, lock the slide back.
I would suspect that CZ mags would function well in the Witness, but not vise versa.
Not that it matters anyway as brand new, 15 round, CZ-75 mags are available from CZ-USA for $35.