It looks to me like the only main difference that might be important between the Value and the Premium series is the clear stage containers. Is this true? If so, is there a good reason to prefer these over the opaque (and cheaper) Value series? I have no experience with RO/DI units.
I will most likely be using this for a nano tank to start with for a year or two before moving up in tank size. I probably will not install the unit permanently in a location... just use it for several hours 1 day a week to fill a large container.
As far as I understand, the clear container contains DI (De-ionisation) gel that needs occasional replacement. This gel changes colour to signal this need for change. The units that I have seen that dont have a clear chamber are just Reverse Osmosis (RO) units and not RODI. This would account for the $ difference... I am sure that someone else will correct me if I am wrong...