No I am not using this but your post made me curious so I looked at the info on the link.
This looks like it will only save you water if your RO unit is connetect to/fills up a pressurized holding tank (tank with a bladder that gets compressed to supply water pressure when the tap is opened).
If that is the case, then yes it looks like a good idea.
I just have my RO/DI filling up a 30 gallon barrel for my reef and then I by pass the DI and fill up 5 gallon jugs for drinking.
