Just got the Sound Professionals velour pad from the Massdrop deal, and yes they are more comfy than the stock pleather pads on the M50x. However, as mentioned before - BE PREPARED for the reduction in bass quantity. For my ears, the bass becomes significantly less impactful. If you are a bass-head, velour pads are probably not for you. Compared directly to my quarter-modded Grado SR60 (circa 2007), the M50x's w/ Sound Professional pads have more emphasis on treble, with less emphasis on mids and bass (although the bass is still tight - just doesn't have the umph like it does stock).
Hopefully that helps with what to expect. Sometimes a change in SQ is not a bad thing, just takes some getting used to!