Do anyone have experience with the efficiency of air ventilation cooling systems for idle parked cars? I know some cars in the more expensive range (Mercs, and BMW's and some Toyota's) have a built in function to regulate temperature function. BUT I want to know, specifically, if the solar-powered ventilation systems for cars are efficient in terms of the rate of exchange of hot air with cooler outside air. And if not how can one try to increase this speed of exchange?
Background: Basically it is said that it is a small vent that enables you to ventilate air from idle/ parked cars by mounting the small contraption to your car window. It uses solar energy to run a low voltage fan that exchanges hot air from inside of the vehicle with cooler outside air.
The reason for my question is to find out if it is worth while to purchase one of these for everyday use in hot countries like South Africa. I came accross some bad reviews of people saying it is a dud, and it only makes the hot air flow around in the car, turning it into something like a convection oven.