This is actually a tricky math one if you want to know whether this is real or not. The question is if you get charged for using reactive power in your home. I think the answer is that you do not get charged for reactive power, only real power (yes, these are technical terms). If you were charged for reactive power, this may indeed save money. It is just a big capacitor that is designed to perform power factor correction. Any local sub station has banks of very large capacitors designed to bring the power factor closer to 1. So if you buy this you are just doing the power companies job for them.
The part about this that is totally ridiculous is that the amount of capacitors you have connected would need to change depending on what you have running in your house. This device is not sophisticated enough to measure the current into your house and therefore cannot calculate power factor and so the amount of capacitance you add is just a guess.
Sorry for the long-winded answer to a stupid device.