This model was imported briefly by Atlas during the late 60's / early 70's. Post-Atlas, Rivarossi occasionally included this caboose as part of their multi-car sets (available well into the 1990s).
More recently, E-R Models contracted Rivarossi to make a special limited run of these models in ten different livery schemes -
The quality of the paint on the E-R Models release surpasses all the other releases by a wide margin. The only other difference that I can detect is that the three little roof doo-dads come uninstalled.
The Atlas imports are stamped "Atlas" under one of the trucks. The E-R's have no such markings. I've never encountered any of the post-Atlas / pre-ER Rivarossi cabeese, so I'm not sure how those might have been marked. In any case, regardless of who was importing/selling them, they're all the same model. Rivarossi was liquidated in 2006, so this caboose is no more.
The wheels are metal and the couplers are body-mounted Rapidos.
These models are based (more or less) on a Southern Pacific class C-40-4/5 prototype.