You realise how inefficient they are when you load it full of warm beer and run it for a few days and the beer isn't even cool yet. From that 60 watts of input power, you only get ~4 watts of cooling, and with some leaking through the walls of the box, the time to cool down something of substantial mass can be weeks.

That's why you have to use a real fridge to do the work before starting the journey. And at that point, those electric fridges are only slightly more useful than a pile of ice packs.