Jay14, the metal plates are to slow the train down incase of a roll back, this is done magnetically. If you watch just before the launch they move down, the ride launches and then they pop up again. If you look, the same metal plates are on the brake run but these don't move. The reason AT would have chosen Hydraulics over LIMs/LSMs is because magnetic launches require a lot of power and are expensive to run. And anyway, hydraulic launches are just as smooth and more efficient, look at TTD and others to see their effectiveness.