This curious contraption is, for want of a better, term, a magazine magazine. Yes thats right, it is a housing that stores a stack of pistol magazines against a spring loaded plate that serves to shift them all along one every time one is removed such that the point of egress remains constant. Instead of having to reach for a slightly different location for your magazines, you can simply reach for the exact same position every single time.
The Tek-Lok bracket on the rear is designed for attachment to MOLLE rigging but could easily strap onto a decent belt as well (albeit slightly less secure due to the size of the bracket).
The Kydex one-piece nature of the housing makes it highly robust, definitely one of the toughest pieces of kit to have crossed our desks. This device will fit just about any type of pistol magazine with the number depending on the exact type ad orientation of said magazines. A Velcro top/side plate can shift to enclose magazines anywhere from 10cm / 4 inches to 18cm / 7 inches long though the most stable Velcro positions are for magazines 15cm / 6 inches or less in length. The Velcro is highly quality and has an enormous area providing an incredibly strong attachment. The carries load spring is very strong and so will strap down your magazines very securely but of course will cause them to rub together with significant force when extracted so your magazines will see increased surface wear (which will not affect performance, just the prettiness of the finish).
To give you some idea of capacity, it will fit 5 Hi-Capa 45/40 magazines and about the same number of Model 17 / Sig 9mm magazines. More square profiled magazines work best, flatter single-stack models may work and even double the capacity but might be less stable. At 35mm / 1 3/8ths inch wide, this device will take appropriately deep magazines so standard pistols ones are fine but will of course not handle rifle magazines.