Thanks for the feedback! I agree with this:

That's a tiny amount of power for the price.

The article points out that it's something like 100 times less efficient than solar energy (which is already pretty low in efficiency). But it's a prototype. It remains to be seen how it progresses.

w.r.t the device effecting temperatures, I guess it depends on where it is placed. If the energy that's harvested would otherwise be lost to space anyway, which is what typically happens with night time radiation, then it wouldn't have any effect on temperatures.