According to APS, the rest is designed to improve the stability, safety, and accuracy of a handgun. It seems to do a very good job as you can see in the video below.
The founder, Rober Gilmer also makes it very clear that since this is not attached to the pistol in any way, it does not count as a stock. The pistol simply rests in the device and your own hands hold it in place. The video below demonstrates how the dynamic rest is not actually attached to the pistol.
In this video we get to see a demonstration of the increased accuracy of the pistol when using the device.