I just thought I'd address the Samhongsa portion of the question. Samhongsa, whom was a major brass builder, is no more. They produced the first two genesis steam locomotives (I don't know whether it was a 100% Samhongsa engine in an Athearn box, or what the relationship was). The list price for the 2-8-2 was $140. I got mine for $100. I saw them for $90 when new. (all prices in US $).
The 2-8-2 was well received, aside from its dummy front coupler. A variety of detailing articles followed it. I never got the Mainline Modeler article on an NKP 2-8-2...but wanted to. The 2-8-2 ran very smoothly, but was a sub-par puller. Mine had a propensity to derail in places no other locomotives ever derailed...some problem with the lead driver.
The 4-6-2 was a failure. Every person I ever talked to said that it was almost useless due to its lack of pulling power. What was there, a 5yr gap in between its release and Athearn's next steam locomotive...I believe it sent them back to the drawing board. Regardless, I still wouldn't mind acquiring one.
Athearn's re-release of the 4-6-2 is going to be under the Roundhouse name. It's supposed to be out soon.
An important note regarding USRA power: the models are of as-builts. Some roads left them in that state until the end, others radically altered their appearance quickly. As an NKP fan, I can state that a few NKP 2-8-2s remained relatively stock...but with new number boards & headlights...while others barely resembled USRA engines.
Mine survived a nasty trip to a concrete floor. I lost a tender marker light, broke a tender truck, broke the pilot, and knocked off both my replacement headlight & number boards. A little glue but everything (but the missing marker light) back together quite nicely! Mine is an approximation of NKP 587 but without the R22 tender.
Here is a post-wreck picture: