I never use it... don't have parasitic problems... and have fecal floats ran by a professional to check load and ensure the right thing gets used... which has NOT been needed yet at my location with my stock density, etc.
Without testing both before and after... it's simply a false sense of security to me... with regards to internal parasites. Even the package says it doesn't work when wet.... as in inside the intestines.
Many birds will carry some parasitic load and it may never be found out. Healthy birds with proper nutrition have a far easier time fighting these things off and keeping them in check.
I can appreciate that you have no symptoms... and ask, sincerely... if you are using DE to treat internal parasite load... and it is working for you... PLEASE have before and after fecal floats done and share the scientific results... Stop the neighsayers like myself! I simply want proof and not assumption since most species will NEVER be seen in droppings.