First TVSS actually uses power as they draw a small amount of load current, which I have never heard of a claim that they can save power (are you sure we are talking about TVSS?)
For all the other snake oil out there, mostly cap banks that they try to claim saves you power, but the power that they claim it saves you is not even billed for in residential, and even if it was (PF) most houses don't have enough motor loads to even collect much for it, and even if this was industrial you wouldn't want the cap banks at the service, although they do use them there, the most efficient place is at each load sized for the load.
do a search on here (if it will work for you) on snake oil, and you will pull up allot of threads on the subject.