Welcome rlh1.
The problem with all of those jar type fly traps....they don't trap the kind of flies that are a problem for us and our animals. There are hundreds of different varieties of flies and they eat different things. Some are attracted to sweet things, some to the aroma of death, and some to the blood of a living animal. The jar type traps you can buy for a few dollars are baited with stinky stuff that attracts the type of flies that go after dead and decaying animals. By replacing it with apple juice you will attract flies that like sweet stuff - but neither of those types of fly is the biting kind that you really want to attract. So - the traps are essentially worthless.
Flies have big eyes but see differently than we do - it is more of an infrared type image that they see. Biting flies home in on a warm animal more by sensing the heat it is putting off than by seeing it as we "see" things. So - the type of trap you would need to catch and kill biting flies would have to "look" to them like a warm, live animal that has blood coursing through it. Such a trap has been invented but costs around $5K
so is out of reach of most of us. About the only people that have them are the big commercial dairies - and maybe some of the racehorse farms in Kentucky. If money were no object, I sure would love one - especially when I'm getting swiped in the face by the cow as I'm milking