I have used one for years during the summer months. In our climate, even with bug spray, there are the big bomber flies that seem impervious to chemicals of all kinds.
I really like them. The only downside I could see to them is that if you need to carry a crop or whip, it will be hard to manage a fly whisk on top of that.
Also, you may have to desensitize your horse to the whiskāsome horses are a little leery of the fact that your arm has suddenly grown a tail!
My current fly whisk is a County. Iāve had it for at least five years, and have taken no care of it at all. It looks essentially new. BTW, when I google ācounty fly whiskā it comes up as having an ivory-colored shaft and a brown whisk. Mine has a brown shaft and a more roan-ish whisk. So I think thereās some variation in colors.