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.