I aint got a RO unit but I heard RO man is meant to be decent [think seffie swears ny them].
Also from what I've heard 4 stage is meant to be pretty good!
I had a look at your link and it looks like a nice bit of kit.
Regarding marine tank keepers, RO units are a god send so go for it. [I would if i had the cash lying around!] lol!