i use them in combo with dust, sticky traps and scent traps. they seem to work real well. the best suggestion i've seen so far is to put the eggs in a paper sack (after appropriate hatching point) hanging on something near the area where the pooh is so they don't get eaten by birds and other things.
i "feel" they work real well. i'm close to neighbors and the flyies are early this year, going to start predators tomorrow actually.