Yea bronco I think has citrenella(sp???) smell which will make the flys want to stay away for a very short while but it is not potent enough to kill or keep them away. I use to love endure until I reliezed it didn't really work. I agree with everone that ultra shield works best and pyranha is next!
Its much cheaper to buy the concentrate and mix it yourself their are actually only a few chemicals that are used in the premix and its deluted to much. Only use fly spry when I ride, my horses freerange on plenty of pasture so they need the flys to keep them in shape, theirs a good chance they would founder, if it werent for the horseflys to keep them running.
I've done fly predators, fed garlic and neither seemed to do much. As others have said, the flies seem to become immune to certain sprays. In my area of Southern Cal, Ultra Shield and Tri-tech which had basically the same ingred. Seemed to work the best last summer. Don't know what'll work this year. I tried all the herbal/organic ones and they didn't help at all.