To be honest, I do not much experience with a rotary, but have always achieved perfect results, though have never worked on black. The blacks I was talking about are the really soft black paints. Other people who have much experience have said this about soft blacks. I know I have never had any swirls whatsoever from my Flex 3401, and that it will correct swirls left behind by a rotary. Based on the fact that rotaries can leave swirls and DA's do not, and that softer paint is more vulnerable to marring, I believe that it is possible that a Flex can leave behind a better finish than a rotary can, and noticeably so to the discerning eye on really soft blacks. Ok, with regard to your work on that 2008 Mustang, phenomenal work! Sorry I didn't praise it earlier. Awesome. However, I would remind you that you weren't buffing BLACK paint, you were buffing CLEAR COAT on a black base coat car, which is a huge difference. Single stage black paint is much softer than any clear coated black.