I tried the greengard and found it hopeless...horse just pushed it to one side no matter how I adjusted the proper headcollar.
Waste of money IMO.
I have a shires one. My horse couldn't eat out of it either at first, but I made more holes in it and that seems to do the job fine.
I tried a traditional leather muzzle, but once it gets wet, the leather goes soft and the horse is as well wearing nothing!
Best friend is good, but a lot dearer than the shires.