I had a 40 40 HF5 from Gaps, never been 100% happy with it. I've had it pumped, unpumped and had it in various addresses with differing water quality. Short story is it was pumped to 80 PSI, TDS in 170ppm , TDS out was 20 (ish) ppm. Just bought this from Vyair.............
http://www.vyair.com/scripts/prodView.asp?idproduct=190It produces water from 170ppm input and the out put is 3/4ppm and that is pumped with one of these........
http://www.machinemart.co.uk/shop/product/details/051012200If i switch the pump off and just go on the tap pressure (40PSI) then the TDS rises slightly to 5ppm, although the fill time/production rate is REALLY slow.
Thats my experiences with them anyway.
Another thing i changed about the way i do it, was previously i had a 10 inch 5 micron sediment filter and then a 10 inch carbon filter. I probably left the change time too long at every three months. A carbon filter is good for 5 micron anyway, so now i use two carbon filters, so hopefully if i change them more regular it should stop chlorine getting on the membrane and damaging it.