Is Elon Musk’s “Pro Power Save” device an effective technology for lowering electric bills, as advertised? Is there a downside?

This is an effective device, despite your skepticism here. If you think about this, you will realize this individual would not risk his reputation and status as a resident genius and innovator of all things technological, by promoting a gadget that is only wishful thinking and a waste of money, but rather something with utility commensurate with its origins. Namely, who is behind it, and that is the point. It is like an ad for his prowess, even though that is grooming you and the populace who come across the ads and discussions about the technology to believe in him as a force for good, that does not mean you cannot take advantage of a good thing despite its origin being a kind of setup to gain your trust. That, indeed, is what it is, after all, a carrot that is on a stick. Just keep in mind, sticks can be withdrawn and not everything coming from this source will be trustworthy. This is the second warning, in fact, we have given. In the meantime, this would be a benefit for anyone paying for their electrical power usage, and can be utilized to good advantage as a cost-saving device.