i usually just urinate on my frozen windshield. works like a charm...although passers-by often point and laugh at the wierdo (but i'm used to that).
since water boils at 100c and that crappy tire doodad heats the water to 60c, i dont think it would damage a cold window. not sure how well it would work because i havent tried one, but i'm sure it appeals to some people.
of course, with an acvw, most of the frost on the windshield is inside the car, so we still need a fix for that. (urine doesnt work...i've tried

)