Even for the more "primitive" 3d printing metal techs, they're just lost wax casting where the original mold is 3d printed. So the results are no worse than any other lost wax cast metal.
The problem with lost-wax and other molded metals is that the fatigue strength is much lower than forged or machined parts. Tolerances are also much looser because the tolerances from each step - wax positive, ceramic negative, poured positive, etc. add up. Fatigue life might not be an issue for a model airplane engine, but it is a safety issue for anything carrying humans.