We used fly predators for a few years, then one year thought they were not helping that much and didn’t start with them, the flies told us different, they again were bad, we ordered again and have since.
For us, while more or less effective over the years, not using them is definitely worse.
The local cattle feedlots use fly predators a carton in every aisle and around the buildings fly bait and their control is sure adequate to very good, given the open air circumstances.
Before fly predators they had to fumigate all every week, spraying insecticide over everything.
We went from many flies around the house entrance, on the door frame to using fly predators and practically no flies there and from horses stomping around during the day to quiet horses now.
They may not work every place, but worth giving them a good try, they may work for you too.