If it were me I would buy the $100 one it has more stages, and you could replace the membrane and still be cheaper then the other unit. RO units are very easy to install, tap a water feed, place your waste line and start filling your containers. The most important part of an RO unit is the membrane and most of the good units use the same high quality membrane, so it really doesnt matter which one you get just be sure it is a high quality membrane.