My take on the whole parasite issue:
10% of the animals in a flock or herd will carry 90% of the parasites/disease. Consistently cull the weak or problematic animals from your flock and you will breed forward for resistance.
Provide good varied free range, and the birds will seek out natural anti helminthics to self treat. My birds skeletonize the rhubarb leaves in the fall, but do not touch them at any other time of the year. I let a lot of my garlic scapes mature. The chickens LOVE those little bulbils and hoover them down as I am attempting to sow them in my orchard. How often do you see birds eating long, rough blades of grass? Ever pulled one of those blades across your palm and watched your palm bleed? That memory is etched in my mind from my child hood days. I bet those rough blades in a chicken gut act as an antihelminthic.
Of course there are not studies that point out the antihelminthic properties of natural herbs and other plants. There is no profit to be had. Pharmaceutical companies would rather push a packaged product that only they produce. These companies are funding the studies.
Good old Basic H soap is one antihelminthic that is rarely mentioned, and it's not possible for the parasites to develop resistance. Farmers were using soap to good effect long before the shelves at the feed store were lined with pills and potions. Mama tossed out her dish water with all the little bits of veggies left at the bottom of the dish pan. Chickens sucked down those sudsy bits.
IMO, a bare soil chicken run is one of the greatest causes of disease and parasites in a chicken flock. The fecal compacted soil is so contaminated that plants won't even grow there. Turn that run into a deep litter affair, and the beneficial organisms will proliferate to help keep the pathogens in check.
Do your homework. Read the published literature regarding natural antihelminthics. I posted quite a list of written material quite a while ago. But the nay-sayers said that b/c the literature was based on human studies, it was not pertinent to poultry. I would rather do a trial with natural approach before dosing my birds with the offerings from the feed store shelves.
I would consider mixing up a potion of garlic, and ginger in the bird's FF. Or perhaps treating them with Basic H before reaching for a pill or potion from the feed store.
Good soil and range management, appropriate culling, and keeping the flock off compacted runs is a good place to start.
One other comment: Why call something snake oil if someone has testimony that says it works? If the individual is not profiting from his testimony, I consider his words to be perhaps MORE valid than the study that is paid for by the very company who stands to profit from the sale of their product.
Finally, if you are truly concerned, have a fecal float test done, and only treat your flock if the float results indicate that there is a load of parasites that is clinically significant to warrant treatment.