I wonder about the utility of a 30 round mag as an owner of a Glock 23 with a CCW permit. It’s bulky enough without the extra long mag. But I recognize that others might disagree and who am I to argue.
With practice & extra mags Jared Loughner could have gotten off the same number of shots. Banning hi-cap mags isn’t going to make anybody a whole lot safer.
You could not conceal a Glock with a 30 round mag in it. BUT you could conceal a Glock just fine with its regular mag, and have the 30-round mag sitting vertical in your spare magazine holder on your other side. My attitude would be, if I'm going out anticipating the possibility of needing to swap mags, I want the new mag to be a BIG mag.