This is a good thread on the topic, and the attached chart shows the salt savings will be minimal at best, probably not worth the additional cost. Do you have a link that shows the "40%" salt savings? That is a claim I have never heard but I would like to see the math on it. To minimize salt usage, install a system that will regenerate every 14+ days with a 4 pound per cubic foot salt setting would be the best solution for you. Do you have an estimate of daily water usage?