I purchased a five stage typhoon reef keeper on ebay from the h20guru. I have has it for 3 months and so far am very happy with it. It has a sediment, 2 carbon blocks, membrane and then DI. It also comes with a pressure gauge, TDS meter, DI bypass valve, and flush valve. The customer service is great and fast.
I know this really didnt answer the difference but it will give you a unit to look into. The one I got does 100 gpd, which really puts a beating on the DI. If you go with the same unit with the 75gpd membrane he told me the DI would last much longer. I payed 210 with shipping.
Hi-s is supposed to have better silicate removal properties. FWIW I replaced all of my filters in my RO/DI with filters from Walter the H2OGURU from Ebay. His web sight is http://www.airwaterice.com/index.htm. His prices can't be beat.
i too bought mine from the h20guru on ebay and have been very pleased with it. i spent two weeks researching and the typhoon 5 stage was the biggest bang for the buck out there by far.
