Hugely erotic. That top seems to understand how much the cocksucker needs to have his gullet stuffed with thick penis meat. Subs need to feel they are of use to the man. The but muscles flexing with each thrust is such a turn on.
Love to watch his naked ass quivering and shaking as he approaches release, followed by good grunting with his ejaculation. This is one of my go-to masturbation vids for sure.