If I may add a few cents here... All these units do the exact same thing and most function in the exact same way and look like carbon copies of eachother. Every single one of them start with a sediment filter, then a carbon filter (the large ones have two carbon stages, worthless IMO), then the RO membrane and some finish it off with a DI. Some of the ones you buy have crappy filters, but most even use the same RO membrane which is the bread and butter of the system. The filters are cheap and have to be changed anyway sooner or later so it almost doesn't matter which one you buy, they are in fact all nearly the same.

EDIT: texmex, link us to the RO unit. I've known a few member who got a "cheap" eBay RODI and have been very happy.