Sounds like 'snake oil' that seems to work because the instructions use the parasite's life cycle to indicate a cure.
The parasite will spend 3 - 7 days feeding on fish and then drop to the substrate, hmmm in about 10 days the fish appears to be clear of Ich. It must be this MIRACLE herbal remedy!
Now the non-visible life stage of the parasite begins and lasts about a month. IF during that month you do some water changes and reduce fish stress, the fish may become healthy enough to fight off the next attack that comes about 30 days later. However, you still have the parasite in the tank and living off the fish (in the gills where you don't see it) until the next stressing occurs. Then wham it start over again.
That is one way to go if you swear to do water changes religiously, not overfeed, not overcrowd, (no vacations) etc.
Or you could use one the only two proven methods to rid the fish and the tank of the parasite; copper based medication, or hyposalinity.