It's very hard to test or even determine the performance of such things as mouse feet because they don't primarily affect technical data like sensor performance if applied correctly and of the right size. That said, I think I have found a pretty good way to demonstrate the difference between the stock and Corepad feet by setting up a makeshift testing table with my laptop. Please note that this is far from scientifically accurate, but it highlights the general difference in friction between stock and aftermarket skates. The two mice are basically identical apart from their cables. I'll let the video do the talking:
As can clearly be seen, the DM1 FPS with stock feet needed a much steeper angle before sliding off the surface of the laptop. The DM1 Pro S, on the other hand, slid off pretty quickly after I started the tilting process.
Something I've also found is that the Corepad set for the DM1 feels utterly smooth from the beginning; the glide is just insanely good right away. The Skatez on my G PRO Wireless, on the other hand, didn't really seem to get near this smooth after a few days of heavy use. Don't get me wrong, they're still better than the stock feet of that mouse, but are for some reason subpar to the DM1 feet by default.
My initial thought was that their contact edges aren't rounded down enough, which might be causing a bit of a scratchy feeling, but that is not the case as their edges are perfectly, smoothly curved, and they are thick enough for the bottom of the mouse (and the feet sockets) not to touch the mouse pad. As such, I'm convinced they either need some more time to break in or are just simply like this, and the glide's smoothness can vary between different feet.
One of the best attributes of these pure PTFE feet is that they don't gain friction with wear—on the contrary, once they really break in, they will remain very fast until they completely wear out.