Cartridge razors are safer only when installing the blades. The cutting surfaces of single blade cartridge razors and DE razors are largely the same. Single edge and injector razor designs were answers to the same problem.
More importantly to Gillette, however, is that they control the patents on each new cartridge design they come up with. The patents on DE razors are long expired. As such you must use OEM or licensed blades in your Gillette Fusion but I can use any blade in my Gillette Super Speed.
