Whenever I do ONR washes (which isn't very often), I use the 2 bucket method still with grit guards. I know Scottwax is a firm believer in ONR and he uses just 1 bucket.
Personally, I don't like using mf towels to do my cleaning pass when using ONR because mf towels hold onto the dirt and grit, no matter how much agitate against the grit guard. I'd use another wash media that releases grit better. For me, I prefer sea sponges or grout sponges. But if you were constantly switching towels, that wouldn't really matter. But then that adds more time, by having to constantly grab new towels, more towels to wash later, not to mention a lot of towels getting soiled badly. I'd save the towel for the drying passes.