Price aside, I like how smooth the crayon glide on the surface. You won't have to worry about scratches if you are drawing on your window surface. We have used them on mirrors, our glass doors, plastic sheets and on this day, we were drawing on our glass coffee table.
My boys love to draw roads, houses, and move their cars around.
The drawing smudges easily so it can your hands and arms quite dirty. But I love the washability. It cleans off easily. See how my boys had a great time cleaning after we finished?
Disclosure: This is a personal review and opinions are my own.