I thought the same BUT it don't do what it says on the box, just changed my membrains after 12+ months and thats with two carbon prefilters on.
So I am now working on the idea of changing the carbon filters more often i.e. every 4-6 weeks for the merlin filter and every 2-3 months for the extra 30" filter I have firtted,(I use about 800 ltr aday x 5 days)
The problem with reading the specs regarding the Merlin is that it was designed to service the domestic on demand drinking water and the commercial uses seem to be an ofspring due to the large volumes that it can produce,
Another thing that I now do on a weekly basis is to flush out the merlin for about 30 minutes (to do this remove the waste water connector from the body and shut off the pure water outlet)
I,ve come to the conclushion that regarding most thing connected to WFP that things wear out quicker the more you use them but the more you use them the more profit you make thus the real expense is still very low, the other thing you have to get used to if you recently moved from trad window cleaning is the amount of money that you seem to be constantly laying out compared to the occassional new bucket,squegee and rats tail