DE isn't manufactured. It comes from the earth, being fossilized algae. It's long been used for treating of internal parasites and external bugs. It's also a great source of certain minerals and vitamins. Because it's not manufactured, I doubt the research into it's use is very biased. People resell it because it works, not because they manufacture it or say, "I want to become a DE merchant". I think they'd pretty much have to believe in it for that to happen. If you use it, be sure it's FOOD GRADE and not the one with the clay added to it like Stall Dry. The clay is added for it's extra absorbent properties and that's okay for bedding but I wouldn't use it for consumption. My birds have had no illness and are shiny and healthy looking and are virtual laying machines with nice, thick shells on their eggs.
Take it for what it is.
Take it for what it is.