These devices are all total rubbish, sold by many different names - Powervolt, Trustvolt, Ecowatt, Trustpower, Motex, Voltex. They do not save any energy so they cannot save you money.
They are an example of the "Big Lie" -see the Wikipedia article on "Big Lie" for explanation.
The principle is that if you want people to believe your lie, you need to make it a really really big one, with lots of supporting lies, because normal people find it hard to believe anyone would be soooo dishonest.
Dave Ward, Chartered Electrical Engineer, UK
PS I know a Nigerian prince who has £20million that he want to smuggle out of Nigeria. He needs some help and is willing to pay a lot. Anyone interested?