Sometimes I wonder if the clear prefilter housings are just being sold to help sell more prefilter cartridges. I think maybe the filters could "look dirty" but still have plenty of life left in them. Not that clear housings are a bad thing, but the best way to know if the prefilters need changed is to measure the pressure drop from their input to output. I read an article that discussed this point a while back but can't seem to find it now. Having said that, I'd still prefer clear filter housings, but I'd also want a pressure meter I could stick on the lines to check the filters.
One thing that is nice to have in an RODI system is a bulk DI canister. You can mount the bulk DI canister vertically with flow from bottom to top which pretty much prevents channelling of the flow through the bulk DI. Bulk DI is really cheap compared to the prefabricated cartridges. The DI canister needs to be clear since the DI is made to change color when it becomes saturated with contaminants.
Last thing - get the dual in-line TDS meter from ebay or somewhere. They are super nice to have, you can see what the TDS reads when coming out of your RO memberane and then coming out of your DI. This will let you know how your membrane and DI are functioning at a glance and is 100X easier than using the handheld or pencil style meters that you have to dip into a container of water...
Also nice to have a 3-4 gallon pressure tank, so you always have several gallons of water available whenever you need it. I would not want to go without the tank since I'm often filling up buckets of RODI water for something or other...
LASTLY - systems often come with a final carbon filter that is in-line after the DI. Ditch that, it's useless for tank water, it's geared for "drinking water taste enhancement".
I have two RODI units that came from
http://www.aquasafecanada.com/
They sell on ebay as "aquasafesystems"
http://stores.ebay.com/The-Aqua-Safe-Pure-Water-Shop and their products are less expensive on ebay usually.
I have not had any trouble with these units, they are working great for me. I use one for drinking water and one for the aquarium.