Has anyone tried this or anything else like it?

http://www.burpee.com/shopping/produ...19&itemType=PR
ODUCT&iProductID=719

I think it would cause the plants to over heat, by magnifying the sun rays.
Yes, I know this is just to be used during cooler temps, but in early spring
you get those peak warm days. Will I have to remove this during those days?

Cheers,
Jim