I use Grand Hoof w/MSM. I have a tb who had very flat feet when I obtained him. He has been on the Grand hoof for about 10 months and he feet are dramatically better. Lots of growth for my farrier to work with and no change in personality. The Grand Hoof w/MSM comes in a pellet form and my horse has no issues eating it. Cost isnt bad either, I usually spend a total of $60 and it lasts 80 days.
I also use Venice Turpentine on the bottoms of his feet every 3 days to harden them up. I put Corona on his coronary bands to keep them from getting to dry. Last but not least I apply Farrier Barrier to also keep his feet from drying out and kill the nasty stuff that can creep into cracks. My wonderful farrier recommended all these things and I am super happy with his feet now.
I have never tried fly boots but I fear my horse would pull em off and chew em up for fun.
I would definitely suggest a fly sheet to help reduce stomping because of flies. I've had amazing luck with Saratoga Horseworks Saratoga Summer Turnout. It's very light weight and yet durable and keeps my horse fly free and happy.