Just to chime in here, I have the Typhoon III from airwaterice.com I replace the carbon filters annually, the sedment filter and DI
resin quarterly (or as needed) and I just replaced my 5 year old membrane. A TDS
meter is a must.
I prefer the clear cannisters or at least a clear cannister for the sediment filter so you visually see when it needs to be replaced. AWI reccomends a 10 micron seidment filter, followed by a 5 micron carbon, followed by a 1 micron carbon before the membrane. I also have the color changing DI
resiin but only change it when I see TDS
Also, the 100 gpd membrane only has a 90% reject rate while the 75 and 150 gpd membranes are higher.