Today I built up three Sonoff boxes which will be used for controlling various mains things. The two smaller black boxes used cheap extension leads. The larger box with two sockets uses an old IEC lead. They work well and are easy to use with the phone app, however, I will be eventually replacing the firmware on these so that they don't have to connect to AWS every time I want to toggle their state. Something with a local server and state tracking would be much more responsive and reliable.