The MA props are more flexible, which means that when the engine speeds up, the prop twists and the angle of the airfoil tends to flatten out a bit. When a prop does this it looses "grip" on the air. The good thing about a flexible prop is that they are more forgiving, and will generaly tolerate most prop strikes, which makes them better for beginers. APC on the other hand is much more rigid, and does not flex much. This means it gets a really good grip on the air and you get better performance. But because APC is so rigid and brittle, they tend to break with prop strikes.