A major reason we went for a Mach 3 head is the way it attaches to the handle in a really neat way, whereas most other head attachments are a lot wider and not so nice looking with lots more plastic! The Mach 3 blades are also cheaper which is good.
Here's an interesting piece about how good the blades are. Thanks Eric! http://thesweethome.com/reviews/best-manual-razor/
It might be something we can do in the future but it would need a totally new handle because our handle is all cast in one piece.