The girl topping clearly isn't experienced with strap on sex and doesn't have the muscle movements down, but it's still hot and they're both gorgeous.
I have to brag. This reminds me of a threesome I had once where I was fucking a girl from behind while she was fucking another girl missionary style. Hot as hell and we all had a great time.
My wife has actually had sex with more women than men, and I've gotten to watch her plenty of times, but she's only ever used a strap on a couple of times and I never got to watch her use iut. Pity, because I know she must rock it!