i am very very wary of these products , you will still need to treat for tapeworms and encysted small redworms as these do not show up on a worm count, what sort of management routine are you on??
if you have a "closed herd" on clean ground that is regulary poo - picked you could just worm strategically for tapes - spring and autumn, and worm in late nov - earley feb for encysted small redworm and use worm counts over the summer and only worm when the count suggests it.
TBH i would rather use counts and chemical wormers when needed that trust verm -xi am led to believe it only repels worms anyway.....
i use Ellen Collinson's Parasite Out, which is the best of the herbal wormers imho. i did my 5 horses with it a couple of years ago, and then had a panic about whether it was effective or not, so worm counted them all - zero for every one.
however, i bought a filly who turned out to have a tapeworm infestation - i double-dose strongid-P'd her, and gave her Parasite Out, then vets did blood count and faecal count, and both were high even after all that.