I personally love grazing muzzles. A muzzle means my horses can be out grazing 23+ hours per day. Without them they would be strip grazed (trashing my natives pastures in the process) or locked up for extended periods, which for gut and mental health is not ideal either.
But they come with their challenges. They can rub if they don’t fit properly. If you don’t have one your horse is OK with they can create behavioral issues (rearing while trying to put them on or being impossible to catch to put them on) and I find certain brands can be too hot to wear in hot climates.
And of course there is always that unknown of how long you should leave one on for your particular muzzle+horse+pasture combination (which if you are like me causes a bit of angst for a while until you get it figured out!).
The other thing you need to be really aware of is how they limit normal behavior. My horses love to groom one another, but with muzzles on all the time they can’t do this. So I have to consciously make time to let them have muzzle free time together so they can do some mutual grooming.
Just something to keep in mind for those of you with muzzled horses.