I only have a fairly cheap single F or Eb French horn (depending on which tuning slide I use), so maybe these are a better fit to double horns, I don't know.
It needed quite a lot of stretching to reach around mine, and I was worried it would do some damage by squeezing the thinner coil of the horn towards the thicker one that it had to go around.
It also felt a bit too thick, and seemed like it would restrict my fingers. Also, where the edge folds over the other end, dug into my hand slightly, and didn't feel comfortable.
I have found a use for it though. I've put it on the main bow of my tenor horn (leading to the bell), to give me a nice grip to pick it up by, when I take it off the stand. I wouldn't have bought one to do that specifically, but I quite like having it there, now I've got it. Maybe it will help protect it from knocks too.