Remember the rating is for 24 hrs so thats about 2 gph under the best cicumstance. RO does waste water, some places like carwashes recycle their "waste" water and use it in other places during wash where mineral content is not an issue. You could collect and repressurize (not that difficult) and use this for cleaning, watering the grounds, flushing toilets...... you get the idea. Just be green with the waste water.
That one you posted is pricy for what you get, You should be able to find it about two thirds that price on the web. I know if I bought 25 of them I could get them for about $125.