I used one in a demonstration at a Boy Scout Camporee, it worked good. I made a peach cobbler in it. The best one I built was this one
http://www.angelfire.com/80s/s.....sided.html
covered in mylar. I cooked chili in this one.
The only drawbacks to solar cooking are you need good sun and they need constant attention. But it was fun showing the boys what could be cooked with the sun.