Well, here are my unscientific results:
Sprayed the herd 8/22. The group at the lake got Fly Ban, the group in the south pasture got a mixture of 10% Permethrin mixed with canola oil. Using
www.domyown.com as an example, 1 gallon of Martin's Fly Ban is 120.17 or 111.92 for 2 or more, 1 gallon of Martin's 10% Permethrin is 67.87 or 62.37 for 2 or more. A gallon of canola oil is less than $10. I mixed 32 oz. of Permethrin with the oil, the Fly Ban is a synergized, ready to use.
First pic was on 8/26. The cow on the left was sprayed with Permethrin, the cow on the right, Fly Ban. No difference/no flies. 2nd pic, same date, sprayed with Fly Ban. 3rd pic was today (8/30), same 2 cows as in the first pic. Yup, they're getting some flies, but not covered, still no real difference between the Permethrin/Fly Ban. 4th pic, also today. Both were sprayed with Fly Ban and have considerably more flies. It's always been my experience, some cows are simply prone to attracting more flies, and it doesn't seem to matter what their body condition is. Things that make you go "hmmmmm?"
Keeping in mind, the heat index has been up to 104 and yesterday we finally got rain, so it was a sweltering 84% humidity this morning and flies are always worse when it's humid & rotten hot. Nothing keeps them completely fly-free over 10 days in these conditions. This is the first year in, well, I can't remember, when we haven't had a lot of ticks, so I don't know how effective just the permethrin is against ticks. But, it appears I'm wasting $$$ on expensive, name brand sprays - and even the homemade knock-offs (aforementioned Grit's recipes; 1 quart of PB08 is $51.21).