As an engineer, I'd be very interested to know the material properties of the printed metal parts. (i.e. the tensile strength, shear strength, compressive strength, and the typical failure strains.)
My employer is just wrapping up some long-winded evaluations of 3D printed aluminum, titanium, and stainless steel, each of specific alloys from a specific 3D printing machine. (Each alloy, printer, and process technique gets somewhat different results.)
Generally speaking, a given 3D printed alloy will fall into the same vicinity of strength, elongation, hardness, etc. as the same alloy produced by other means (billet, bar, casting, etc.) If you 3D printed Ti-6Al-4V powder, it can have about the same properties as billet Ti-6Al-4V, give or take a bit.
However, there tends to be more scatter in properties in 3D printed parts. Even after trying treatments like hot isostatic pressing and tempering/stress relief/aging/annealing, etc., you get more scatter. The major reasons for the scatter are:
1) There's always more porosity in the final part than a conventional stock metal because you're welding together powder, and
2) You're basically working with a big piece of weld metal
Prior to heat treatment, there's also some variation in strength by direction. A specimen is stronger along the direction of deposition than across layers. My experience is that there's much less anisotropy in 3D printed metals (a few tens of MPa difference) than in 3D printed plastics (factor of 2 tensile strength difference between longitudinal and transverse directions), but that's speaking to specific 3D printing techniques. You can't fix the 3D printed plastics, but heat treating, especially HIPing can help metals.
There's also surface finish to consider. None of our evaluation parts went straight from 3D printer to Instron tensile tester or Charpy impact tester. The exterior was so rough that it was basically a stack of weld beads. So it went from 3D printer to CNC machine tool to finish the test specimen and then into the test rigs. Using the raw, printed metal would've had different properties before the polishing and prettying.
Basically, treat a 3D printed metal part with the care and concern you'd give a weldment or thick casting of the same material. It's more likely to have flaws, brittleness, and reduced elongation compared to properly worked billet material, but none of that means it's unusable and uncorrectable. With a good testing program, you can get A- and B-Basis mechanical properties for 3D printed metals that your designers can depend on.
And results are improving steadily - the 3D printed metals today are nothing like the porous, brittle crap from the 1990s.