That roll on stuff hasn't been very effective around here.
I have found the best stuff around here is Pyrhana. I only spray them down when I'm riding, and only the spots they cant' get with their tails. Petroleum based sprays will scald the horses skin if it's put on too often. I had that happen with one. Having a shed they can get in is the best thing for when they are out loose. Only little house flies will go in a dark shed/barn. Keep the stalls mucked and that will thin them out.
Becky
Well, I won't waste energy trying to find the roll-on if it doesn't work!
I don't spray them ~often~ either. I use the masks you've seen to protect their faces, and that's about it. Only when I've had them haltered for baths or something and I've got it handy, do I spray them if flies are around. I really don't have many flies.... no more than any house has. I have found the best fly management to be poo management.... I spread their manure every day in both the paddock and the pasture. Flies breed in fresh manure, if you can spread it fresh, it will dry out before they can hatch in it.