I've been using them for 3 yrs now and wouldn't live without them. I didn't realize how great they worked until after the last shipment last fall. We had an unusually hot fall and I had houseflies for the first time about a month afterwards. I added more shipments this year (and more animals) so hopefully it'll work out.
I free range my chickens and ducks, so I hang the open bag in a tree near the paddock so the chickens don't munch them. I also pour half of them in the big manure pile that's far enough away that the chickens don't reach it.
I do wish they worked on water breeding flies and mosquitos as well, but they almost completely eliminate the manure breeders for me.
I should also say that the company is very easy to deal with and they will work with you on an individual basis to determine what will work in your situation. They also stand by the quality of their product and do guarenty(sp) live shipments.