
I think you cannot say it is just as effective as modern wormer's will treat the larval stages. the natural one may be effective against adult worms and make the environment unpleasant, but I don't think the makers make any claims to it being as effective as the likes of Panacur or Drontal.
As for fecal samples, if we tested Rather than wormed which is what most US breeders I am in touch do, you would find that most of the samples are negative. We overuse wormer's just as much as over vaccinate as it is cheaper to worm vaccinate than pay what are vets charge to titre test/test fecal samples.
Most adult dogs will be negative for roundworms (assuming adequate worming when pups), which are primarily found in puppies, lactating/cycling bitches and those in close contact with these.
Our preocup[ation and fear of Toxacara are mainly due to the anti dog lobby latching onto this issue which hasn't been used so much in other countries.