Any unit will work just fine, I would recommend a 100GPD membrane, and make sure you have DI resin in there somewhere. All the other features may be fun but historically turn out to be not that accurate and to stop working over time...the two units I use now are both bare bones, all produce 0 TDS. I recently bought a few units from the site below, they are in stock and ship quick, they will even do custom stuff at reasonable prices.
http://www.maxwaterflow.com/