I use the paddle, which comes with the kit. You have to install it but it takes like two seconds. I like it a lot better than the belt for easier adjustment.
I hate blackhawk's hype and marketing bs, and the fact that they are not actually level II retention. However, I greatly prefer the serpa level I system on the CQC to standard thumbreak holsters as I find them clumsy. Also, the serpa lock is more secure IMO.
theoretically I think the serpa lock is a better retention method against a grab than a thumb break. a gun grabber probably will not quickly figure out how to unlock, while a thumbreak is obvious. This is a very important consideration when OC'ing. True Level III would be ideal here, but I think CQC is a good compromise.
Quick criticism: the body side wall of the holsters have a piece of polymer that I can easily get to pull the trigger on a glock if you re-holster too quickly at an improper angle. It can happen even easier if your shirt or a fold of your shirt slips over the edge of the polymer. Very dangerous if you do not take care when re-holstering with one in the pipe. BE VERY CAREFUL. It would be stupid of you if you caused an AD/ND this way, but Blackhawk could have easily made this piece larger so that it would not fit in the trigger guard of the glock.
I use CQC on my glock 23, my FN 5.7 and for 1911's. All are comfortable (Except 1911 at 3 oclock on me), easy to draw, and secure when riding ATV's and the like. Never had any malfuntions. BTW, I love it for the 5.7.