The poster you answered is completely right.

Actually Philip these solar cookers turned out to be pretty pointless for most of the international agencies that tried promoting them too.
Even with the best technology and the ideal economic environment for them they were failures in the end. The only places they saw much use was at refugee camps in equatorial areas of the deserts. Places where the people had nothing except the sun to use, not even camel dung.

Solar cookers do not free you from other cooking systems, and once you get above the 45th parallel solar cookers are nothing more than interesting school science demonstrations.

And the windshield reflectors work well for designs like the Kookit.