I am looking to buy a RODI unit today. I have narrowed it down to the Buckeye field supply Chloramine unit and today only BRS has their 6 stage deluxe unit on sale. TTL out the door both units are the same price with all of my add-ons. In your opinion which unit is better/more functional. What is the purpose of having 2 di resin cartridges? Please need some advise asap. Thanks in advance.