OK, but it's a lighter weapon to start with and I have a shoulder sling for carrying! They will accept the smaller G17 9mm Mags too! And since I'm not going on any 30 mile forced marches anytime soon the weight isn't an issue!
I have mounted a similar magazine holder to my S2K. It works really well for the G19 & G17 mags, but since it is really only a friction fit, the 31 rd mags tend to work themselves out if you are putting yourself into any real world moving about. With mine, my left hand is holding the mag and foreend while the S2K is deployed and I am actively working the course. It is when the S2K is folded and hanging freely on my sling that the loss of the 31 rd mag is possible. It looks great, but I think in a real situation where we may need to take cover and the like, we may loose the 31 rounders at the wrong time . . . . .