[White95Max]

The original Propels have a 5" diameter depression on the back of the pad, and that makes it incredibly easy to center the pad perfectly every time IF you have the 5" backing plate.

I agree though, I'd buy all 3 of the backing plates. They all have their place. I'd recommend picking up some of the 4" Propel Turbos as well, to use with the smaller backing plate (2.75").