I have tried magic shave, and in my experience it does not get as close as a razor blade, but similar to an electric razor. And some people are sensitive to the chemicals in magic shave so if you try be cautious and do the spot test first.
My suggestion is to continue with the razor shaving. With practice, you should be able to get the time down to something less than 10 minutes, and the magic shave will have to stay on your head for 10 minutes to work. As to cost, a tube of magic shave costs about the same or less than two fusion cartridges, and you will get about two to three full headshaves out of a tube, so it is more expensive to use.
Try to find a less expensive razor to use that gives the same results as the fusion. I use the Persona M5 and the Micro Touch. I can get two weeks out of a cartridge with daily shaving. I shave in the shower and can now shave in less than 5 minutes. It may take you 6 months of daily shaving to get your shaving time down to this, but you should be able to get to less than 20 minutes in 30 to 60 days. Although my hair is thin on the top, I have a full head of hair to shave, so I am not skipping any areas.