As I see it, this is good for low power iOT devices that are installed in remote / hard to reach areas (say underground etc. ..). A small temperature difference could produce power enough to run the device without any battery.

Heart Pacemaker require around 10uWatt and this new power source seems to provide 12uWatt for 1 cm2. If temperature difference could be maintained, then could provide a low weight, low power source that do not require changing battery.