"This motor is okay by itself in either the 10219 Maersk Train or in a custom train of yours. But if you REALLY want to see your train go, get 2 motors as well as the 8869 Power Functions Control Switch. (In the Maersk Train, you will have to take out some bricks to fit the switch, but it doesn't show at all on the outside.) This will allow you to put 2 motors on your train, and lets one motor run forward while the other runs backward, all while using the same knob for the throttle. A $15 upgrade TOTALLY worth it.
Using one motor, you get decent torque and traction, and good top speed. However, on speed 1 it can't really get around turns and slows down a lot on turns in the higher speeds. It also starts to slow down when you add more than 2 cars.
But if you add a second motor, your train will be able to pull EXPONENTIALLY more cars, and even reach a higher top speed while pulling cars. In fact, you may want to not use the top speed, because sometimes the locomotive will uncouple from the rest of the train while moving, and if the locomotive is pushing cars, it has the tendency to push them off the track on curves. If you want to use the train on the top speed, use cars with low centers of gravity (like the ones that come with the Maersk Train).
The only reason you wouldn't want this cheap upgrade is if you don't have many cars. I have tested the train with all of my 7 cars (and I want to test it with even more!!!!!), and it runs just as well as it does with only one motor pulling two cars. Overall, it's the best upgrade you can get for your train."