I believe the MDC Roundhouse models date back to the late 1980s. When I get a chance to verify this, I will update this first paragraph. These models were some of the best bang-for-the-buck you could get in N Scale at the time. They were simple toolings, with only one detail part; the brake wheel. Furthermore they were in kit form, but unlike the headache presented by InterMountain kits due to the number of detail parts, these models had no detail parts (except the brake wheel) and hence no headache. The kit form again shaved money off the price tag. Lastly, Roundhouse had the very well received habit of running more obscure road names that nobody else would touch, often in multiple road numbers!
MDC Roundhouse really made it a point to "own" the 50' boxcar. They had thirteen different 50 foot boxcar toolings all from the transition and early diesel periods. Each mold had prototypically correct details that set it apart form the others. I am not expert enough in the prototypes to say how accurate any particular model was, but with thirteen different models they were bound to have something more-or-less accurate for just about any mass-produced 50' boxcar of that period. Also at that price point, NTRAK folks would buy a lot of them for their long unit trains.
Unfortunately they hit some hard times and in 2004, they sold all their N Scale toolings to Athearn. Many folks were sad because they figured 'Rats! That's the end of my hope to see more Lamoille Valley rolling stock...." Fortunately for us enthusiasts, not only has Athearn been re-releasing these cars, but they have also made some improvements.
Almost all of the changes affect the bottom of the car, so let's take a look at two FMC 50 foot boxcars from an upside-down perspective.
Top = Athearn, Bottom = MDC
The first thing you will notice is that Athearn has decided to paint the underframes. MDC has always made a nice underframe with plenty of detail. By making it out of metal (pewter?) they obviate the need to add weight to the car, which keeps things simple. Ever had a weight come loose inside a boxcar? Annoying. It always struck me as odd that Roundhouse would do really nice paintwork on the bodies of their cars but for some odd reason leave the underframe unpainted. Why? In any case, Athearn decided to fix this and now the underframes are a matte black.
The next major difference is that the couplers are now body mounted. This typically leads to better operating performance as well as making the cars look more prototypical. Many manufacturers have started updating their toolings to switch them to body mount from truck mount, and it is good to see that Athearn got the memo (if only they would fix their milk reefers...grr).
One final difference is that while both wheelsets are metal, the Athearn wheelsets are just flat out nicer looking. In the photo above, the trucks are swapped for MTL truck/couplers on the MDC model so you can't see what the original wheels look like, but trust me, the Athearn ones are nicer.
As I stated before, many of the manufacturers are updating their older toolings and this is nice to see. I would expect to see a new version of the MTL PS-1 (20000 series) boxcar sooner or later. It does appear that almost every new tooling carries body-mount couplers and metal wheels. Many manufacturers are also augmenting their older models with metal etched details for end platforms and other separately applied details. This was not the case for this release, but I am just happy they are making the effort to update and re-release this venerable (ok maybe an exxageration) product line.