Ditto on that Viesczy. I have a P99 9mm. Got 2 16 round SW99 Mags for it for about 30 bucks a pop and they have in 1350 fired rounds functioned absolutely flawlessly. The Walther marked ones are 45 a pop and for some reason hold one round less. Except for that they appear to be identical and MecGar is the manufacturer for both Walther and S&W mags anyways so the quality is the same. I guess it just boils down to preference.
Walther Forum Member #55