Porting reduces felt recoil and muzzle flip. The longer the barrel, the better it works, and the bigger the ported area, the more effective it is, e.g., quadra porting is better than just dual porting.

I've experienced it on my own revolvers. And porting has never caused lead spitting for me, but that may be because all my porting was done by the gun manufacturer or a reputable company rather than some local well intentioned amateur.

I love my Model 637, 2.125" barrel PowerPort with compact-sized Pach grips and Hornady CD +P loads. The single large port at the end of the barrel doesn't dirty up my drift-adjustable front white dot sight which sits behind the port. The barrel is too short to produce anywhere near the maximum effect of porting, but it's better than no porting.

Louder to a shooter? Don't know, I wear hearing protection.

Less velocity? No, not compared to the normal velocity from the slightly shorter length barrels on standard S&W snubbies. Besides, any loss of velocity compared to a non-ported barrel of the same length would be insignificant; less than the differences in velocities caused by differences in B/C gaps.

More flash in low light? Not when I use Hornady CD loads, which is all I use anyway.

Better control for follow up shots? Yes.