The finish on the black M9A3 will be exactly the same as the finish on any other black 92 variant (like 92FS, M9, 92A1, etc)
Honestly - in 9mm, the buffer on the 92A1 doesn't do much. Yes, the slide is a bit thicker around the locking block, but not in the same was as a brigadier. And, it really doesn't matter. However, the sights are dovetailed, so you can change out the front sight (unlike a 92FS).
I have owned a few 92A1s over the years. I prefer the M9A3, though. For one thing, it comes with night sights already on it. That's an added cost, if ya wanna put that on later. Also, the M9A3 comes with a factory D spring already installed, and it has a metal trigger and safety levers. I also like the FS version of the M9A3 - the levers tilt up at a higher angle, which makes it harder to accidentally put the gun on safe.
The 92A1 is cheaper up front, though. If you never intend on getting night sights, get the 92A1. If you do plan to want night sights - just get them on tghe M9A3 to begin with.