I will be honest. I always thought these type of sun shades are stupid. My mom used a product just like this with her car. It didnt work well I feel at all. I remember one day saying to her "um mom you know you have four side windows and sunroof and a back window right?" Now these guys that have the sun shade that covers ALL the windows would probably work and be the way to go.
I second this. I have owned several of these over the years. (S2000, Integra, 3rd Gen Prelude and Honda Fit). The only car that didn't have all tinted windows was my Prelude and it was less-effective on that car. The rest were all tinted and with this windshield shade it helped dramatically.