Not to put the thread back on track but....
I have a similar RODI unit with the drinking water storage tank and faucet but without the dual di. I bought it off the same ebay seller and it's made by the same company. Works great. Water in is near 100tds, water out the drinking faucet is 2tds, and 0tds out the di.
The dual di is nice because as the first one begins to change you can swap out it out with the second one and then refill the first and put it where the second one was. You may have to change the fittings to john guest at that point to make it easy as pie.