More is better. Even if you don't use them, you can keep them as spares. Who knows what kooky laws will pass in the future.
For my M&Ps, I have a FS and a Compact. I really only have 4 Compact mags (1 flat, 3 pinky), but I've got a bunch of FS mags and 4 Xgrips to use my FS mags in my Compact. I also have a Shield. I do need a few more for it.
Of course, ymmv. Being in CA, we're limited to 10 rounds so I have extras to make up the overall capacity difference for units where the "normal" cap is over 10.
For my M&Ps, I have a FS and a Compact. I really only have 4 Compact mags (1 flat, 3 pinky), but I've got a bunch of FS mags and 4 Xgrips to use my FS mags in my Compact. I also have a Shield. I do need a few more for it.
Of course, ymmv. Being in CA, we're limited to 10 rounds so I have extras to make up the overall capacity difference for units where the "normal" cap is over 10.