Are ear bonnets suitable for fly protection when horse is turned out in pasture?

I use the mesh fly masks that cover the ears as well. They are not too hot for the horse and if caught or snagged on something, they will come off. (Some come with double velcro so it's harder to take off, but they will stiff come off in an emergency.) They work well as long as your horse does not get annoyed with it. My mare has no issues with hers and it stays on all day and does not make her too hot. However, the clever little gelding in the pasture next to my mare has his off within an hour of being turned out. The gelding is partially blind, so I am not sure if he takes his off so he can see better, (Why his owner puts one on him if he has bad sight as it is... I don't know.) or if it is because he is just a goof and won't leave it alone. So it depends on the horse really, but I find the mesh masks that cover ears work well for my mare.