I bought the Bi-tone because I thought it looked better than the all-black. I'm not a shiny kind of person, just liked it better.
I don't carry, so whether it announces its presence or not is not a concern. However, if and when you *must* use your gun for self defense, I don't think it makes much difference whether it's shiny or not.
In any case, SS has been easier to maintain so far, and wear doesn't show as much as the black slide.