I once had the box in the car for about 6 hours in the blazing sun. Of course, the box can't keep the temperature constantly low, but I was still pleasantly surprised at how well the coolness was maintained. All in all, I'm very satisfied and can get by without a compressor cooler. However, if you need a constantly low temperature, you probably can't do without a compressor box.

As is usual with thermoelectric (piezo) coolers, the temperature that can be reached depends on the ambient temperature. This means that if the ambient temperature rises, the achievable internal temperature also rises. The possible differential temperature depends on the design.
The Tropicool is comparatively efficient and, according to my measurements, reaches approx. 20°C below the ambient temperature. In a cool basement room (16° C), a minus temperature can therefore be achieved. It's a different story in a hot car.
I usually put 2 additional cool packs cooled to -20°C in the box when using it in summer and in the car.