Last year, Tom R posted about these mag pouches at SHOT Show 2015. I got to see them out in the wild.
At the 2016 FN 3Gun Championship match last week, I ran into Larry Houck. He was the match director for FNH USA 3Gun 2011-2015. He showed me his new Blackhawk quickmod magazine cases. They are a self contained user adjustable magazine pouch.
Most quick detach magazine pouches are limited to some sort of two piece docking mechanism like the Safariland ELS system or they are some sort of molle system.
The Blackhawk Quickmod system is an adjustable clamp for direct attachment to any belt. On top of that the magazine pouch can rotate 360 degrees for personal preference. This comes in handy for competition shooters. I see many pistol shooters orient their mags in different angles to facilitate faster magazine reloads.
The quickmod pouches can fit single or double stack mags. Larry was using them for his 2011 pistol magazines.
Here is a video briefly explaining these pouches.
The mag pouches retail for $40.95 for pistol pouches and $50.95 for their AR15 mag pouch.