ESSTAC has made a name for themselves with their hybrid Cordura/Kydex pouches. ESSTAC is known for great quality and fantastic modern shooter solutions.
ESSTAC front panels do not come with the Female QASM buckles.
To use Esstac's front panels on different plate carriers that are out on the market make sure you have the 1" female buckles and they are spread 6" apart from the inside of the buckles. Also make sure your carrier has loop velcro under the buckles so their front panels can attach to your plate carrier that you have.
Front panels are removable via velcro (they act as the cummerbund flap) and two ITW QASM Buckles at the top. Simply pop the two buckles and swap panels. They are built the same as Esstac's normal Kywi pouches, but instead of Webbing on the back for mounting they have Hook velcro and two buckles to integrate into the PC.
Front panels remove some excess typical of Plate carriers, no longer do you need a mounting system and front flap. So you remove some weight and streamline/thin the front of your PC.
Quad 556 is a wide pouch, best used on Large plates only. It will overhang on either side(about 1") and is best used with the cummerbund ends out to the outer edge for more grip of the velcro. This option is for those that need that extra mag up front and can live with the downsides.