These things do nothing a 30 cent capacitor can't do, and are completely useless in a residential setting. You just don't have enough motors starting up for them to matter. Because that's all they can do: correct the power factor of a cheap motor.
Residential kilowatt hour meters "ignore" power factor, and only record real power consumption. So a homeowner's electric bill will not be reduced by this device. It only makes sense to use at an industrial customer, where the power company does measure power factor along with real power consumption.
Oh, it might help if you connect a cap across a motor on a circuit (reducing reactive current) that is maxed out (breaker trips out after a while), but code may dictate better solutions to that sort of situation.
