Sometimes you can see the stuff with your naked eye, too, if you have good eyesight.
You can definitely see an edge that's been stropped once vs. one that's right off the hone. I usually rely on that. If I can see the very edge of the blade has been worked by the strop, it's rare that the shave has that bite. I don't know how good everyone else's eyesight is, but mine is not scheduled to go south for another 10 years if family history is an indicator (last test at ER when I got metal in my eye, it was 20/13 in the bad eye (the one that had a metal particle stuck lightly into the middle of the pupil).
But, anyway, horse butt has taken away that super sticky sharp edge that I used to get when I was obsessed with honing extremely lightly on clear water and then stropping extremely likely. I have felt since then like a strop that will dull your razor if you use moderate pressure is just too soft, because moderate pressure on a tight horse butt strop does nothing but improve the edge. On my cowhide strops, it definitely takes a lot of their keenness away, but that may be due to something other than the fact that it's just cowhide (maybe it's the tanning and maybe it's because they're not broken in enough, but they're just missing that support that horsehide provides).