I pretty much bought this purely for aesthetics to match the brass block of my gotoh trem, not for sound. I didn't really do any extensive AB testing comparing this and the original, but sound and sustain didn't really seem any different, no increased "warmth", no seconds added to sustain. Being analog instrument, there of course is likely a difference when changing parts, but if there is any with this, it's pretty negliciable, but then again, I play high gain 90% of the time so the difference could just be lost in the gain.
Reading the other reviews and knowing that brass is pretty soft metal, I didn't even consider using the included brass screws and just opted to use the original steel screws, not wanting to risk having the screw snap in half and embedding itself into my guitar.
All in all, it's a little bit silly upgrade since the trem cavity is rarely visible and atleast I didn't get any sound benefits, but it's pretty cheap so it's not a big investment.