I do not speak for the D&SNG or any other associated parties that have done business with MP&ES, but some of the work they do is less than stellar. They are most famous for doing repowers and rebuilds of diesel locomotives, I believe both of the butt head switchers owned by the Charleston SC Port Authority were done by them. New builds of anything, especially two customized locomotives like the two ordered by D&SNG is no small task, but was probably more than what MP&ES was capable of.
As for their quality, I have seen pictures of both units and I would be embarrassed to say that my company sent both of those out. Never mind the appearance, but the fact that simple things like the height of the fuel tank to the rail head and the frame ride height off the trucks were not checked or accounted for is absolutely astounding to me. As a matter of fact, I think MP&ES rushed the engine bodies and frames to Durango in the first place to avoid being sued then but I am not sure.
I think both of those locomotives would make good units if they were to be fixed properly by someone who knows what they are doing, but then again some of that would involve botching things together, and for the amount the railroad paid for those units I would not stand for it one bit.