I wonder how this works. Maybe it only functions when it detects the wall has 120V power? If it backfed during a power outage it would be like plugging a generator into your house with a cheater cord (never, ever do that) which can step your generators 120V back up into 12-25kV through your local transformer and zap the linesman working to fix your outage on the neutral (a generator backfeeds onto the neutral not the “hot” sides of the circuit. I.e. the “safe” wire suddenly has thousands of volts on it)