I use a grazing muzzle for my IR mare. I love it. I have the Best Friends Deluxe model, and it is secure, comfortable, and lasts quite well. I have to have her in it any time she's in the pasture, so I wanted one that was easy to breathe in and drink in. Also, if you have to completely restrict grazing and do not have a dry lot, there is such a thing called a 'grazing plug' for a grazing muzzle that is designed to block the grass but NOT the water! The horse always needs access to water, so the 'plug' is nice because it has a lift with the pressure of the water that allows it to flow into the muzzle. I would, however, only use it if you can't take your horse off grass and must restrict eating, and I would make sure you are home to supervise. Some horses may not try to drink with it in even though they can. Action Rider Tack sells them.
I like the Best Friends model because it doesn't rub and it has a nose channel for easier breathing. Also, I noticed in her first muzzle she was able to wear away the rubber at the hole quite quickly, whereas she's had this model for six months and the hole is just as nice as it was when we got it. It's more expensive, but you get what you pay for. For as much as my mare wears it (anytime she's in grass), I like it.