If you're using a single wash mitt or sponge I think it's absurd not to use two buckets unless your car is already pretty clean. I know all the old ONR marketing talks about flocculation and pulling dirt to the bottom but who is really rinsing their wash mitt/sponge so gently you're not kicking up dirt? My hot take is those who use a single bucket + BRS are usually staying on top of washing their car so there's never a ton of dirt floating around to begin with, and it has less to do with the magical properties of ONR (not that ONR isn't great!). Change my mind
Also I think if we're getting nitty-gritty you can't look at this stuff in isolation and just as important is what you're doing
before you touch the car (rinse/pre-soak/touch-free tunnel/worx hydroshot/praying to the car wash gods)