Good advice all around - especially from Anit77 and EnderG.
The manifold is pretty standard. Clear canister on at least the sediment housing is nice because you can SEE when it gets funky.
You can get sediment cartridges for $3 (ask me where...) - keep that and the carbon block changed often and it prolongs the life of the membrane. Dow/Filmtec membranes are the best, but there's less than 1% rejection rate between it and say, a CSM membrane which is considerably less expensive. Colour-changing DI is nice (with a clear housing) because you can see when it's exhausted.
I also like to have an HM Digital DM-1 inline TDS meter on any unit. I personally configure it to test TDS on unfiltered water and filtered water. Some put it before and after the DI, whatever floats your boat. With that, regardless of what kind of system you have, you can push a button and find out what your TDS is and that is an indication of whether your cartridges need to be changed.
The trick with RO and RO/DI is water pressure. All membranes except low pressure (LP) membranes are designed to work best with 65 PSI across the membrane with water at 77 F. You can't always control the temperature of the water (do NOT run warm or hot water through a membrane). Pressure is something that can be adjusted and if you have low pressure a booster pump is a worthwhile investment.
If your pressure is low, your ASV (auto shutoff valve) may not work properly and if it takes longer than it should to filter water, you will waste more than the 3 or 4 gallons of brine (wastewater) to 1 gallon of permeate (filtered water). You can also get a permeate pump which is non-electric but recirculates the water through the membrane, to boost pressure.
If you have any further RO questions, PM me for more info if you wish.
Oh and anything more than a 4-stage system is a waste, IMO. You need sediment, carbon, membrane, DI. If you're using it for drinking water too you might want an inline carbon post filter too, but that's about it.
Jenn