Kent RO unit question

I've gotten a Kent Hi-S RO unit from a buddy who has gotten out of keeping
fish. He said this is a 35 gpd unit, but I'm not so sure of that. It only
takes it about 4 hrs to fill a 13 gallon container, so I wonder if it's not
actually a 60 or 75 gpd unit.

How long does the membrane in this unit last? Marinedepot website says 3 to
5 yrs, but they want to sell more, so wondering if that's a low estimate of
the useful life for the membrane?

Thanks,
Mark