I think it's fantastic that you can rub the bottom of your heel on the pumice stone, and the sides of your feet heal up! Reminds me of adverts for toys - the damned things never performed quite how they did in the adverts, e.g. Evel Knievel bike.
Call me a sucker, but I want one of these. My 5-year-old would finally want to wash his feet. (They should have one for an entire 5-year body, actually, to just squiggle through.) But mostly, It looks like it feels good.