I also have the Kent RO/DI Maxxima Hi-S business, but got it used for 50 bucks when buying live rock from a guy breaking down. If I bought new, I would go with the cheapest unit that offered 1 micron prefiltration, 5 micron carbon block, 90 gpd or larger membrane potential and a DI cartidge, with a TDS meter, auto shutoff valve and pressure gauge. The unit needed new filters and a membrane. It had a 35 gpd membrane and flow restrictor when I got it. To save water, I got a 90 gpd Spectrapure membrane, and another RO canister with another 90 gpd membrane to install so that they ran in tandem, not in line. This doubled the output, lowering the waste to product water ratio, now I get my 50 gallon reservoir filled faster while saving $$ on the water bill. I added a TDS meter, pressure gauge and auto shutoff with float switch for filling the reservoir. These units are easy to figure out and most upgrade parts come with great instructions. I used spectrapure kits and membranes. Basically, all membranes are the same, made by the same manufacturer (DOW filmtek membranes). Some companies offer guaranteed rejection rates, but if you are going to do a DI then it will only help to have a higher rejection rate if you want to save on DI resins. I tell you this so that you save $$ and not buy the unecessarily expensive replacements. Kent is way overpriced, for replacement membranes and cartridges (pre, carbon and DI). All units are interchangeable too, so if you want to you can upgrade a smaller gpd unit to a larger by buying the right flow restrictor matched to your membrane's rating. I do wish I had a booster pump now. That would really save me water by making the 40 lbs of water pressure I have higher. I also ran tubing (all JG fittings and tubing are at HD cheaper than most mail orders) into a plastic cooler full of water with a heater set at 70 F to heat the incoming cold winter water to boost membrane efficiency. The pump is the last bit I need. The unit had a flush kit too, which I kept and use for 15-30 seconds before I shut the unit down. The auto shutoff with float switch is the way to go. I highly recommend that. Good luck, shop around!