Yea, I know. I have used them. All those things do is dent up your balsa. And I don't mean where it's supposed to dent it, I mean where the little "guide fingers" slide along the top and bottom of the surface.

Besides, I hate to buy something that I don't need, especially when it's something that only has one use, and is so small that I can never find it the one time I need it.

BTW, here's the sanding block.