I bought the ECO270 over a year ago early for a remodel job. The company was responsive to my issues. I called and left a message and emailed, got an immediate email reply. Even tho I have hard water with no softener, there was no build up in the system whatsoever, but all my appliance and faucets did.
Disadvantages: The only fault I can say about the heater is the sensitivity to water flow/pressure. If you have very hard water and your supply pipes have varying pressures to different points of use, due to large scale buildup in your pipes, you might not like this product.