The US Hobbies (KTM) version was always my favorite. It was better detailed and ran better out of the box than the IMP. Most of this was because it is a newer model. US Hobbies did the original dockside version and also a model of the loco converted to a tender loco with the tank removed.
The IMP version which I had, did not have bearings on the axle. The axle just rode in holes in the formed brass frame. The USH version had bearings and a cast frame. I had the USH version of the tender loco and have seen many of the tank versions. I also had the tender version from IMP at one time.
