We did it and it was great! I'm not the rail aficionado that my DH is, but I enjoyed it anyway. You get to enter the park before anyone (even early ADRs) because the trains have to be in service when the park opens. (We were there in December, so we got a beautiful picture of the Christmas tree on an empty Main Street.) You ride the train into the wheelhouse, see the other trains, get to go into the engine, learn about the trains & their history, and ride in the first car with the engineers talking to you.
It lasts about 3 hours.