Well I have noticed a big difference since I've been using D.E. The fly population has decreased significantly along with the odor. Can't ask for more than that. But I'm opened minded... I'll have to check out these fly predators just for curiousity's sake.
Try the recipe in this topic, "Help with DE doses" I haven't yet but I am going to give it a whirl. Just got the recipe today. Re: 2nd page of topic.
https://www.backyardchickens.com/forum/viewtopic.php?id=5015