I've been using a Mach 3 Power for a while now, so I tried shaving one half of my face with the Mach 3 and the other with the Fusion.
The results were rather disappointing. The Mach 3 actually felt smoother while using it, while the Fusion felt like it was catching on my beard. The Fusion also had a harder time around my lips, the underside of my nose and especially along the sides of my chin.
The end result? Both sides of my face felt equally smooth and both sides grew back equally.
So stick to the Mach 3, the Fusion isn't worth the extra cost.