I think it works, to a certain point.

A friend of mine does something similar with his electric razor blades and some really soft sandpaper (but he has a very soft beard).

Also, would you really be surprised if the dull cartridges can be salvaged and Gillette/Schick just did not care telling us so we keep buying more?

That being said... 200 shaves? Sounds like a little exagerated.