It looks like there's some water softening (adding minerals back in after filtering) after the last stage looking at their website. That's not recommended, the RO/DI portion maybe sufficient (and tap off for your saltwater/topoff) before the "softening". Not the clearest website to understand...unusually heavy in pseudoscience marketing lingo. At it's heart, looks like standard RO/DI unit with re-mineralization (common as RO/DI tastes metallic without it). Proprietary will mean a bit more money, of course. Best course of action would be to have the water tested (ICP or similar testing might be sufficient). As I stated you can tap off after the RO/DI and test that for you or finally you could route after the RO portion and then have that feed into a DI unit (2 or 3 stage) for your tank. That way you can go with bulk resin and save some bucks.
