Guys - here are somethings to look for in a good RODI system for this hobby:
No more than 4 stages (sediment, carbon, RO, DI) unless you have specific water quality issues you want to address
Standard-sized prefilters, membrane, and DI cartridge
Brand name, high-rejection membrane
Specifications provided for each stage
Pressure gauge after the prefilters and before the membrane
Thermometer
TDS meter (handheld or in-line)
DI bypass
Vertical DI stage
Refillable DI cartridge
Aluminum bracket
Quick connect fittings
No water from pressurized storage container delivered to DI
Flush valve
Clear housings
High-quality instructions written in clear English
Customer support before, during, and after your purchase
A vendor involved in your hobby
You'll see that some of the pics above show systems with no pressure gauge, with two carbon blocks although one good block is sufficient, with horizontal DI stages, etc.
Russ