I'm happy to report that they actually do work ...
... right up until the first rousing game of Bite-the-Face.
These lasted 2½ days.
If you have a horse that is pastured alone, or kept stalled, or if you have horses that just stand around and look at each other, I highly recommend them. If you have rowdy, rough-and-tumble geldings like mine, you may as well not bother.
And that's why we don't have anything nice around here.