MagPod is a drop-in base plate replacement for the current PMAG 30 Gen M3 Magazines and previous versions of the PMAG 30. It is designed to make using the magazine as a monopod more stable and to aid in gripping the magazines.
To appreciate the MagPod, you really need to have some background in using the magazine as a monopod.
The 5.56×45 NATO (and .223 Remington) cartridges have tapered sidewalls which necessitates that the magazine have a slight curve to accommodate the stacked cartridges. The end result of the curved shape is that only a small portion of the base plate toward the rear of the magazine contacts the ground when it used as a monopod and the rifle is held level (or near level). You can create a very stable shooting position this way but with only small portion of the magazine on the ground, it is not as stable as it could be.