I have two (ATSF 4-6-4 Blue Goose and UP Big Boy 4014 "as restored") that I'm running where they aren't supposed to be running (3-rail club layout with a 36" sharp curve in the mix). They run well and sound good. I've test run both of them conventionally (on 2-rail track with AC and DC power and they run smoothly that way as well. I also have a 2-rail "imposter" ATSF 4-6-4 Hudson (hi-rail wheels that can run 2-rail) which also runs well on 2-rail track.
The only thing I don't like (technical point) is that they're wired "like" 2-rail steam, but the positive/negative pickup wheel locations are reversed from standard. This shouldn't impact 2-rail operation but it's something to take note of if you have other conventional DC steam.