Like the last couple of posts, I used them for a while but then gave up because while they catch a metric crapload of flies, they attract more than I have ever had around here without them. Having said that, I don't have cows or even a dog, so I don't get a lot of flies normally.
I keep fresh binkills in my wheelie bins (https://binkill.com.au/ - woolies or bunnings) and they work like magic, I always know if I've missed the expiry date because once they're done maggots show up immediately.