I picked up a relatively inexpensive unit on an auction site that has worked well. It's not the fastest unit it terms of output, but I turn it on and let it fill a 5 gallon bucket a few days before I do the water change. No rhyme or reason to this, just the way my schedule works out. Like I said, my unit is slow, so it takes a good couple of hours to completely fill my bucket. After that I add the salt and I do add some trace elements (such as iodine, molyb, strontium, calcium). Not sure if they're really needed but it seems to help.
Keep in mind how RODI systems work. You'll need a location to install the system that has a water inlet (from your main supply) and then a drain. The water flows across the RO membrane and only some of it (a very small amount) goes through the membrane. The rest goes to drain. That is where you'll see differences in output. How much water actually goes through the membrane. This is a function of membrane size, water pressure and the amount of "hardness" in your incoming water.
If you find that your water pressure is way too low (say 20 psig or so), you can always purchase an inline pump to up the pressure to meet the minimum requirements of your system.
In terms of brand names, I'm not much help. I usually look at what I need from the system and go from there and try not to get hung up on names.
jim
