I would ask: Do you feed sugar syrup? If so, is this thymolised (as per Hivemaker's recipe, for instance)?
I have no experience of that product as to whether it is effective or not, but it would seem you may be throwing away money on another of these 'must be better than home-made' alternatives, that are nothing much more than a means of jumping on the band wagon, to relieve beekeepers of as much dosh as possible.
If only precautionary, I would tend towards the cheap and effective 'KISS' option, and if they were infected, I would use Fumagillin as that has been proven to be effective for years and years and years.
RAB