I know people who are really happy with these, using the Staedtler correctable pens. I prefer a regular pad of paper, but it seems some people are made more comfortable working things out on an erasable medium.
Pencils don't do it for me. I find the color of the text written to be too faint for my comfort. Pens on the other hand write text in bright blue color which is I find more pleasing to read.