Multiple blades (4+) on shaving equipment like fusion will make it MUCH harder to add detail to your facial hair as the head become bigger therefore making it harder to judge where to cut the hair. Stay away from the king of shaves blade as that is a nightmare to use for shaping hair.
One good thing about the fusion however is the single precision blade at the top which is excellent for detail, but that alone does not justify the cost for me so I prefer cheaper alternatives like mach 3 which still allows a close shave and the head is not excessively big.
The mirror you use will also help too; I stay away from mirrors which magnify as they tend to distort the image and so causes you to cut inaccurately. I find the best set up to be mirrors which have a lamp as a frame (like the ones in hotels).
Don’t forget that facial skin is very malleable; learn how to move it with your free hand in order to get the detail you want.
Oh yeah you might want to try a cutthroat, as many recommend it for adding fine detail.