I use BOTH DE and sweet PDZ.
Sweet PDZ (or Stall Dry) are horse-stall products that -I believe- absorb and neutralize ammonia to cut down on smell. They have no anti-parasite properties like DE.
DE can be used in bedding, feed, and to actually dust chickens with. My understanding is it's tiny silica (?) that cuts into soft-bodied insects, thereby reducing internal and external parasites as well as fly larvae in bedding. It is also a sort of dessicant, I think, that absorbs moisture to an extent, and in that way also cuts down on smell in bedding.
I sprinkle Stall Dry/Sweet PDZ under the shavings in the main coop, and then use DE there as well, and also the DE goes in the nest boxes, and I make a "whitewash" of DE & water to paint the roost and droppings board with when I do big cleanings. I also add DE to the feed, if it doesn't already contain it (Blue Seal Organic Life, for example, already contains it. Check the ingredient label.)
Hope this helps, sorry I don't have the exact facts!
Stacey