I have the MTH Rail King version and it's been a good runner once I worked out some kinks (bought it used - needed tractions tires, and had some track issues as well). It isn't scale, as has been mentioned, but it is large (and heavy) compared to my other Rail King steamers. When on the layout, surrounded by other RK engines, it definitely draws attention. The nice thing about it is that it will run on smaller radius curves, but it looks goofy on anything less than O-54 in my opinion. It has a nice level of detail (I don't like a ton of detail as I tend to break it...) and the sounds are reasonably good as well.
Like I said, good runner. I keep trying to convince myself to sell it, as it does not currently have a permanent position on my layout, but at some point I always decide to plop it on for fun and then I can't bring myself to part with it. That being said, if you are a "scale" guy, look elsewhere. MTH just recently re-released it in Premier, but no Norfolk Western - I'm partial to my NW!