My boy gets his muzzle half the time. I was worried about him just making up for it during the night, since he's on grass 24/7, but he still has lost weight with it on.
He has a couple rubs on his cheeks, but I'm putting it over a fly mask now. One of his pasture-mates likes to grab it and pull him around, but even still they've only managed to get it off once so far.
But I feel bad for him. Whenever it's on he stands alone, well away from the herd, and pouts. He hasn't figured out how to eat with it on, even though I've fed him occasional treats and some grass through the little hole. He's been wearing it for over a month now, and he seems to have just given up trying. He's a VERY social horse, so it breaks my heart to see him out there alone.
I can't wait until I can take it off again, but for now weight management is more important.