What is the best high UV fly mask available?
Guardian mask ($125) claims 95% UV coverage. I like that the eyes are structured but the one I had in the past was quite stiff all over: http://www.horsemask.com/Products.html
The equivisor ($39) claims 95% UV coverage as well. The design seems good for riding but I find it hard to believe it can withstand extended unsupervised time: https://www.amazon.com/EquiVizor-Horse-Fly-Mask-Protection/dp/B0713W1JWX
The UViator ($60) is 90% UV coverage. Does 5% make a noticeable difference? This one is most like a typical fly mask which seems encouraging for the likelihood of it staying on unsupervised: https://kensingtonproducts.com/products/uviator-protective-mask-90-uv-protection
ESV Visor ($50-130) has a range of products in the 70-90% range. Tons of customization options and sizing, which should make a true fit much easier: https://www.equinesunvisor.com/esvmaxx.aspx