Interesting link, Finis . . .
hmmm, hydroponics in Washington State . . . makes me think "I did not inhale . . ."
Interesting note on the Solar Concentrator on there about an old Satellite dish, too. But the guy used Elmer's Glue? I am thinking this toy should not be left out in the rain, or even dew?
When I was shopping for what would make "good, fast, cheap" mirrors, I had pondered mylar as well. It seems like it would shape very nicely. Quotes I got were typically around 35 cents per square foot, but using mylar means that some other support is needed for it to maintain shape, as well -- so that cost must be added in, as well.
It looked like prices on the link you provided ranged from about 15 cents to around about 70 cent per square foot depending on thickness?
A second matter after price was durability. Estimates I heard were 2 years max, out of doors. Does that seem correct? I think I have seen mylar on glass that lived much longer than that. Like auto tint, for example.
At any rate, between price and rumors of lack of durability, I settled on glass mirrors, but am more than willing to change my mind.