Personally I don't use it. I've always been wary of products that claim to do everything, and DE is one of them. There's also the fact that they state on the package that even food grade DE should be handled and used while wearing a respirator. I'm not inclined to used anything that requires a respirator for humans - an animal with much larger, better built lungs than a chicken - in or a near the areas where my birds live.
Note that if you do use it, you should always use food grade.
I use some DE, but very judiciously.
Get it cheap (compared to other sources) at my feed mill from their bulk stock,
it's 100% Food Grade DE (no clays added as many other 'DE' products contain, read labels carefully).
I put it in all the cracks and crevices under the straw bedding in the nests,
and in many other cracks and crevices around to coop where it cannot become airborne,
as a preventative.
I also use it in and around my feed bins as I have had a couple go rounds with grain mites coming in with feed.
I stage new feed bags on large kennel trays edged with DE in the garage for 24 hours to inspect for grain mite activity,
then mix a bit of DE in with feed before transferring it to my feed bins in the coop.
DE is very effective in this application and is commonly used in animal feeds as a pest deterrent and an anti-caking agent for stored grains/feeds.
We use DE and love the benefits of it. We were very skeptical at first for the fact that it says you need to wear a respirator. So we had done a lot of research and asked a lot of questions... the only reason why a respirator is needed is because it's such a fine powder it's not good for your lungs to breathe it in. But we've been told it's also not good to breathe in baking flour or any other really fine powder. DE may not be good to breathe in but it also has a lot of benefits for human consumption. I have seen many recipes for DE smoothies and such... but have yet to try them.
We sprinkle DE around all cracks of the coop, in bedding, dust baths, nesting boxes, and around the feeders. My husband wears a mask when he does it, I do not (shame on me, I know!).... we do so when our flock is free ranging so they aren't there to breathe it in. I sprinkle it down quickly and when all the doors/Windows on our coop are open. Once the powder settles I open up the gate to our run so they can have access to their coop again.
DE isn't for everyone, but we swear by it. To each their own