This stuff is supposed to work differntly from rainx. Rainx outside makes the water bead off faster. This stuff is supposed to stop condenstation from ever forming. Give it a try, you are only out a dollar or two if it doesn't work. You could also try leaving your window cracked open a bit on a night it isn't too cold, or let the defroster run before you drive. I only usually have this problem in the summer.
