It might make you cringe but my electrologist who recommended me the riffi said you cause tiny scratches on your skin when you use it wet.
Previously, I had tried all kinds of abrasive exfoliation methods from other mitts to fine pumice stones. I had always used them wet, so using something dry was new to me too.
She suggested I use it on dry skin before shower, in gentle circular motions. She stressed that moisturising was just as, if not more important. So I’d use the mitt a few times a week but made sure I moisturised (I used bio oil) daily. My issue wasn’t pepper spots, it was fine hairs on my legs growing in a coil and caught just under the skin. In the past I had tried products like tend skin without much success. For me, a week or two of the above routine sorted out my problem.
I do think glycolic acid products would help as well.