does this imply an overall entropy reduction for a whole system comprising a device and support apparatus for reusing its heat as energy source supply?
Or at least recycle some of the heat fridge/freezers produce back into electricity.
This was already possible. Now you could just do it more efficiently.
It's just a heat engine like any other electrical generator so it's not going to have fundamentally new kinds of applications.
Don't forget you can also use the waste heat from a device (like a computer) to run a mechanical heat engine to generate power to help run the device. But only partially. I guess we don't do that much because it's probably not economically feasible. That's kind of what turbochargers in cars do though.