The hf5 you are on about, works more efficient @ lower tap pressures than the hf4 and will make u water a bit faster if thats the way you want to go, but you would have a higher tds on either, than say a hf4 boosted to 70/80psi, which still makes lower tds water fast. I get about 210L per hr, but my hf4 is about 3yrs old + now and its gone from tap in 420tds to r.o. out @ 10tds to 27 in the last year. So i will be getting a new hf4 axeon £220ish inc del. from gaps, prob after winter now. There is also their hf4 GE AK90 which is supposed to give u a slightly lower tds, but i dont if its worth a extra the £50 on the hf4 exeon. Good luck m