It is pretty much quackery.
There was a good debate on this subject awhile back. (As well as another.)
The subject comes up from time to time, and the studies show that the product does actually work NUTRITIONALLY ... but does zippo for internal worms.
This whole "rough edges of the DE" is only correct when the product is DRY ... and flies out the window once the product is ingested (and thereby moistened).
It is quackery to use it for internal parasites ... and most people don't know how to differentiate between "opinions," claims, and "advertisements" (which can say anything) ... and published scientific studies (which are held to a standard).
Ads and people "claim it works"; the published science says it doesn't.
Jack