As far as I know, phenolic is legal in APA, BCA, USAPL, VNEA, and pretty much every pro tour.
Legality for phenolic is a non-issue.
Without question phenolic hits harder than leather. However, harder is not necessarily better. I prefer phenolic (well actually I prefer the Hammerhead tip specifically, which is a thermoset plastic). I prefer it because it gives me the feeling that I can swing my cue fairly soft and still get a nice pop out of the rack. Also, if I really want to smash them, like I might in 8 ball, it sure feels good. For most breaks, I feel like phenolic type tips offer me more control, primarily for the reason that I feel like I can swing softer and still get a nice hit.
As for jump cues, phenolic is vastly superior to leather. I'd say this is one place where G10 performs very well. The Hammerhead tip is ridiculous for jumping! Amazing. If you want to be able to do really close up jumps, a non leather tip is the way to go.
Be aware, the things that make a jump cue good are not the same as the things that make a break cue good. In most cases they are the *opposite*. The best jump cues have lots of weight right up near the tip, typically using heavy ferrule materials. You *want* a jump cue to deflect the cue ball away from the shaft. A break cue, on the other hand, benefits quite a lot from lower deflection. In fact I'd argue that the benefits of low deflection are the greatest in a break cue (considering that is the situation in which you are most likely to unintentionally hit off center).
I recommend using a dedicated break cue and a dedicated jump cue. The performance benefits *for me* vastly outweigh the convenience aspect of a jump/break.
Today I played in an 8 ball tourney. Mike Dechaine was playing. He broke with his playing cue, hitting the front ball at around 25 mph (which for him is a soft controlled break). For him, I sincerely doubt any sort of break cue would have netted much benefit over what he was doing haha! For the rest of us, the harder non-leather tips can really help.
KMRUNOUT