You can double the speed of a slug and not have it do anything meaningful as a useful domestic animal.

Thermoelectric cooling is extremely inefficient, to the point that we have very little practical use for it right now. Heat pumps a hundred times more effective predominate.

Heat pumps can move a lot of heat efficiently. Thermoelectric coolers can move heat more precisely and in much smaller packages. They don't need to beat heat pumps at their game to be useful for their own game.

TEC are used everywhere, actually.