There is almost NO maintenance for these hydraulic brakes. I went out riding with some friends recently and at the bottom of the hill they all had cramp in their hands, I did not. Of course, I'd be interested in any other comments you might have. As far as I can see the only real disadvantage to Maguras is the cost. Cables, and particularly cables that go around sharp corners, tend to be elastic and have some friction.
Hydraulic fluid can go around arbitrary corners with only minor frictional loss.
If the pipe is good and solid, the system also has good stiffness. As an example, a stick through the spokes is very powerful but has lousy modulation. Conventional cable brakes have much better modulation, but the Magura has even better modulation. The stick through the spokes example points out also that a brake can have too much power. When you go over a bump you may accidentally pull a tad harder on the brake lever.