So has anyone used these? I've heard great things but wanted to hear what other people think on here. Do you really have to release more every few weeks (doesn't that get really expensive?)? Also is there any difference between the brands - Fly Predators and Fly Eliminators? Fly Eliminators has a sale going on right now as per this month's Horse Illustrated and they are less $$ but I don't want to get them if they aren't the same as the others.