We used a grazing muzzle on a mare last summer. She was a percheron/stb cross and was used to being in the barn 24/7. We got her in winter and she didn't abuse the hay but when the grass come out she really put on some weight. She already has a slight road founder so we were concerned. We also had no stall or paddock so we tried the grazing muzzle. She did great and it worked great. She was able to eat all day, drink fine, but not gorge herself. She did manage a healthy weight and the vet said that she looked great. It did have a breakaway feature on it. She did loose it once, it was a draft size and a little heavy and the adjustment slipped some and it came off her head. But she was at our house and we did see her often. We found it very useful and helpful, she was able to maintain a healthy weight and still be out to pasture, and she acclimated just fine to it. Good luck with your boy.