VermX actually creates a hostile environment for worms in the GI tract of the chickens, which makes it OK to use as prophylaxis... however if you have an infestation, you really need a chemical wormer to kill the worms.
If I'm true to my principles I can't actually say catagorically Verm-X isn't effective however the signs aren't that promising since Verm-X make no claims specifically about it's efficacy and they do advise you to regularly take a worm count even when using the product!
The below is a paste from an answer to a FAQ on the Verm-X site. It's the only info I can find which hints at how it allegedly works.
"
Verm-X consists of herbs that have been used for centuries as a natural way to repel and control internal parasites"
Since worms don't actually crawl into chx, they are eaten as eggs and hatch in the bird, I can't understand how they can be repelled. Do the eggs hatch in the chicken and the worms think "it's such a hostile environment in here I'm going to wiggle off some place else" or perhaps they prevent the eggs from hatching? Surely the only way to "control" worms is to actually kill them so why is Verm-X so coy about saying this. Well probably because it's classed as a biocide rather than a pesticide and to get EU approval for a biocide is significantly easier and cheaper than for a pesticide and further more it can be sold over the counter. Biocides are non-toxic and are generally repellents (eg such as a mosquito spray) though as I have said I'm not sure how you can repell a worm. I guess I could also check what the active ingredients are which they are legally required to include on the label and then check what they are used for. If they are manufactuered by a third party as a component which can be formulated in a mixture there should be data on it. I did this for Barriers RedMite powder (and Spray) and found out the active ingredient was a mozi repellant manufactured by a third party who had no data on it's effectiveness for Red Mite though it's mozi repelant charateristics were well documented so you could puff or spray it on yourself as my wife does with the Barrier horse fly spray. Incidentally this is substancially the same as RM spray and uses the same active ingredient. Similarly with the RM powder and Louse powder. The main difference being the label and some avocado oil for their coats in the horse products. RM are a completelly unrelated species from mozis and are more related to spiders than insects so it was highly dubious this would be effective even if it's method of application wasn't flawed.
If I find out more on VERM-X I'll let you know.
HF