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?
i am aware of it. i was not pretending we could reach zero entropy but nevertheless it manifests entropy reduction compared to an energetic non-optimal raw material doesn't it? meaning if we need less energy for the same amount of work we do it more efficiently and therefore require less (but not null!) entropic output
Are you asking if it violates the 2nd law? Of course not.
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.