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