I use citronella extract mixed with fixating oil.
I also use vinegar mixed with water and dawn dish soap.
I have a friend who zip ties fly tags to their horses halter and it keeps the flies from their face.
I love Ultrasheild ex. I works so well. My horse is so sensitive to flys and this very much helps
Feeding garlic helps repel the flies as well.
I use citronella at the mo as that's working best at the moment and also neem oil :) not had any experience with cow tags though, my horse also has a sweet itch fly rug
outsmart by smartpak works wonders
pyranha fly spray. its the best stuff in the world i swear!