David,
If you get one of his units, I would highly suggest the Typhoon III. It comes with quick flush capability so you can rinse the RO membrane anytime (important feature that helps the most expensive filter of the unit), pressure gauge, and TDS meter. The pressure gauge and TDS meter will clue you in as to when you need to change your filters....don't want to replace your filters too soon and waste money, nor do you want to replace too late and hurt your aquarium.
As kipass said ... www ..... airwaterice .... com is where you can find all of walter's units.