The folks at Muddy Hill Farm in Montgomery County, Maryland grow blueberries and raise chickens and pigs. Hence, they have flies.
They recently put two fly traps to the test -- the RESCUE! Disposable Fly Trap and the Black Flag Flying Insect Trap -- and posted the results on their blog.
They posted a comparison of the two, along with results on Day 3 of the test, in this blog post.
And the results after Day 7 of the fly trap test are posted here.
Bottom line: It looks like RESCUE! outperformed Black Flag by three times, at just one-third of the cost.