Yes, I tried it... If I remember right you have to add it to all their feed, daily... continually... ("forever"), and I simply couldn't afford to keep it up. It was too costly (watch out for freight charges on heavy or large items).
DE -- and though I didn't keep it up well, the WormGuard... neither prevents or treats worms in my opinion. Maybe someone else has used WormGuard faithfully for a long period of time and has more experience with it.
Use the Search here on BYC and Search for "WormGuard" and Search for "Verm-X" and see if you come up with much more info, I think you might.
Also Search "Worming" and "Worming with Valbazen" (yes, it's a chemical, but it's a good broad spectrum wormer that kills all types of worms safely.... must be given individually, orally, and withholding eggs.).. look for posts by dawg53 on worming. You can also Search "giving oral medications", and "how much Valbazen to give", etc.
Take care, good luck..