I have an RO/DI buddie and it makes plenty of water for my 29G system. With that said, in the last year I have replaced the DI stage twice so far, and the carbon section once.
I would probably have been better off just spending the extra 50 to 100$ bucks initially and not having to buy 2 DI filters and a carbon block already bringing the cost of the cheaper unit up more so then a more expensive unit which I wouldn't have to have bought 2 DI stages already.