Hi Mark
, I bought the Mantua 0-6-0 T and had to take it back. The frame was curved, so the rear driver wasn't even touching the rail. Everytime I backed up, the loco would derail. But, I understand mine was a exception( wirh my luck, that figures), other people have had no problems at all. When you test run the loco, push down on the cab roof, to make sure the driver is on the rail.
Also, I recently bought the 2-6-6-2 by Mantua, and it runs great. Smooth running and great low speed. Now, all three locos have the same drive, so that gives you an idea of what they are like.
Good Luck.
Loren