I once worked for a manufacturer of thermoelectric modules.

The very laws of nature cause them to be horribly inefficient power hogs. A good thermoelectric module requires a material that has a high thermoelectric constant, a low thermal conductivity and a high electrical conductivity.

God made it so that most good electrical conductors are also good heat conductors and vice versa.

They are good for “uh, compared to what?” types of applications where you need a little cooling over a small temperature difference.

On the plus side, the surface of the ceramic substrates makes a wonderful extra-fine knife sharpening stone.