Thats the one I bought and it works great, but I had a problem when my power went off my overflow lost it's siphon and the pump ran the sump dry. Well the top off system kept filling it up and in turn the tank over flowed not fun. I'm going to put a battery back-up to keep this from happening again.You don't want your auto-top off to be connected straight to your RO/DI unit. If the top off system gets stuck in the "on" position for any reason it will lower your salinity, kill off anything in your tank, and flood your tank if you don't catch it soon enough. The safest way is to use a storage tank that you refill once a week or so.
Here's a top off unit I'm going to purchase soon, it's on sale also:
http://www.drsfostersmith.com/Product/Prod_Display.cfm?pcatid=13959&N=2004+113592