As already been said, it is totally your call if you feel like trading your started 3-year-old for a not started 5-year-old.
I'd really like to see better pictures and better video before deciding on the back end on the 5-year-old. The picture you posted makes him look very "off" in his hind end, and look like his left front foot is turned as well. I'd like to see a "butt shot" and a front shot of him. He seems to move well in the video on a circle, but I'd like to see how he moves directly away in a straight line, and toward in a straight line (so you can see which legs are winging in or winging out), and also see him move in the straight line from the side.
His pedigree .... I don't see anything I recognize. So on that aspect, brownie points for being registered but really no better than your mare with unknown lines.
Have you been running your 3-year-old mare on barrels? Or is that a different horse you are talking about?
∞•*˚ Βгįťţαňγ ˚*•∞
It is not enough to know how to ride; one must know how to fall.