Agree w/ neil, all I've been using for years is a 4 stage, as long as you have a chloramine block you're good, DI is a must, TDS inline is nice, hand helds work fine too, I keep mine out of light and back flush to keep prefilters from clogging prematurely, some have an auto back flush.
BRS makes a very good unit, spectrapure as well, they have a refurb page on their site worth looking at, usually good deals there, but I would not hesitate on a BRS at all.
There's a fine line between owning your tank, and having your tank own you!_________________________________________
120G SCA starfire, tunze 1073.02 return pump, Geisemann reflexx 4xT5, 2x panorama pro LED strips, 2x Vortech MP 20's, 40g sump w/ fuge.