FWIW – I use the 2-controller solution. I replaced an older Hunter controller with OS. The company that I use to do the blowout and maintenance has a Hunter remote module that they connect to my Hunter controller when they do work. Ray gave me the same info/warning about using 2 controllers. I decided to take one additional isolation step. I build a ‘switch’ using Phoenix connectors that allow me to manually switch which controller is connected to the zones. Since I only need to switch controllers once or twice a year, the manual switch works well.