I have always used a brass ferrule on my snooker cue, though I do have a black fibre ferrule on my pool cue - although I don't play pool that often to be honest, but I nevertheless still enjoy the game.
I remember in the 1980s watching snooker as a kid on television to see that many of the Canadians professionals didn't use brass ferrules on their snooker cues, which I guess was an influence from pool. Though it never really caught on in snooker, and although I think Steve Davis may have experimented with a non-brass ferrule on his snooker cue, he reverted back to a brass one.
Quite a few club cues I've come across don't even have a ferrule. The tip is glued straight to the wood. I don't think there's any science in a snooker cue ferrule. It's just there to stop the wood splitting at the business end and a flat edge to glue/trim to.