The idea is good, and I think it holds a lot of promise for probes, particularly smaller probes. But I am skeptical it will be able to control anything with anywhere near the mass that a ship capable of sustaining human life will have. The problem isnt really even control I guess, its the energy needed to maintain control of a large vessel. The mag beam would have to be more powerful than a "megawatt", of that I am positive.
Probes, particularly those going into the farther reaches of the solar system can get there sooner and like they mentioned, the sooner the better because the risk goes down considerably. And, considering that these stupid little probes cant be build with radio shack supplies, I'd imagine that lowering the risk would be the best course of action.
Or thats my opinion.