6 stage filter for $100 is a good deal and you get good water.
However, after brian bought his there have been a couple things we have noticed.
1) You don't get 110 GPD, more like 70ish
2) If you leave the water on and let it build pressure it seems like I was constantly fixing a slow drip, so I couldn't recommend that unit if you were going to hook directly to a float valve.
All that being said... I now bring mine in the house once every two weeks and make my water for the waterchange, fill up the 15 gallon topoff reservoir and all works great. Oh yea and the 20 gallons for you HEHE.
If they are happy with the one they mentioned I would look into it.. There honestly has to be a better unit than what I have, but at the time I wasn't sure RO/DI water helped that much and was more interested in quality water cheap. They threw in the leaks for free :).
Brandon