The only thing I'm really noticing about the buckskin horse is that I think he would make a better roper or barrel racer than the other one. I can't really see the other one too good, but from what I can see, the buckskin has shorter, stockier legs, which is great for getting down low and into the dirt and moving fast while in the dirt.
I don't think there is anything wrong with someone standing on a horses back, it mite not be the most comfortable thing for the horse, but it's certainly not going to hurt em, maybe the rider if they don't know how the horse is. Would I ever do it? Hmmm, not at the moment thats for sure lol but maybe with a little more work I'd think about it.