The thing with any aperture rear sight is for maximum benefit it needs to be positioned as close to the eyeball as possible. The Skinner sight is a compromise in that regard - mounted out on the barrel far ahead of the eye, the eye/brain mechanism doesn't digest the automatic centering of a circle as effortlessly as it would if mounted behind the receiver, plus you sacrifice a huge amount of sight radius which is a factor in accurate shooting. There's a reason you have never seen, nor will you ever see, an aperture sight mounted out on the barrel of a serious competitor's rifle, and we duffers should pay more heed to lessons those fellas learned the hard way.
Don't get me wrong, it's a compromise but not a deal breaking compromise. On a personal level I've tried them and found them lacking.
I know they make one that mounts on the barrel, but mine is the standard receiver mounted sight. I use it as a ghost ring unless I'm shooting paper from a rest. I'm imoressed how fast and accurate the aperture sight is, and how forgiving it is of older eyes