If they can be stored sealed for at least a year, I would buy 4, otherwise 2 per year.

As an aside, I got a price quote from ag-photographic a few months ago. It's over $200 for one kit shipped to the U.S. from the U.K., so hopefully Badger can get the price down considerably from that. I believe the price of the kit alone is over $100 retail over there (including VAT), so it's really the shipping that kills any reasonable chance of an individual importing it.