In my experience it didn't do enough. It was okay but really I felt like I got no better results then I did with other sprays. Now, I did have relatively decent luck with the fly predators but you have to start early in the season with those.
In the end I used the roll on fly replant for their face and 'tender bits' areas and Bronco for the rest of them. And of course fly masks...though stock up. My morgan would scrape his off on the fence posts every opportunity and then run around the pasture killing it.... I should have bought stock.