The only minor flaw I saw at the time was the firebox - it was too narrow,
I have heard this before, but, I never have measured mine so I don't know if it is too narrow or not.
However, there is one major flaw. That is the way the steam pipes are connected to the front cylinders. For whatever reason, being cheap skates is one, they used the same connection that was used on a UP Challenger or Big Boy. Totally wrong!