I have been using Summer Whinnys on my mini donkey for the last week or so. They definitely provide a good fly barrier but I have had some slippage issues with them so it’s still a work in progress. I was really hoping for something to protect his knees and hocks, which most fly boots cannot do. The flies really love the poor guy.
Cashels, which were only slightly less expensive, slipped down on him immediately. For a TB I had several years back, Cashels worked okay and remained functional for two summers.
Another non-traditional brand I considered was Shoo Fly. If I had been able to get them locally in a mini size, I definitely would have tried them.