You didn't state what kind of pistol it is and what finish the slide is in.
If it's like this one, is the slide flat black enough for you? Is so, you can paint just the frame and maybe get the results you want.
I've Duracoated several handguns and they've all turned out and lasted well. I didn't use the shake and spray, though. I used the kit that came with a little airbrush and compressed air can.
I used the shake and spray on a rifle stock and it seemed fine, but it certainly isn't prone to the kind of wear and tear a pistol would go through.