How is the Bondo all purpose putty different from the lightweight filler?

It will not stain. Use a good enamel base paint.

It shrinks, cracks, doesn't sand very well, and is suggested that it is only used to fill a surface no more than 1/8 inch thick. Although it is cheaper than much better products, it is not worth saving a few dollars. I do auto paint and body work as a hobby, and experience has taught me never to use bondo again.