So to drag this one a bit further,
MIM can absolutely be polished.
My preferrence:
Stainless steel finish then bead blasted, Polish trigger and hammer for contrasting against flatter bead blast finish.
I have done it on 2 pistols. a 620 and 686-6. I also had it done at S/W on a 60-10 when they did a complete action job on it. I guess it depends on what you wanted it for aesthetics? I used to have a few picks but deleted them. My current 60-10 and 686 have highly polished hammer and triggers.