The advantages
are about 15% more 'Pop' on the break. My 65 year old big brother was breaking like sh*t, lost his snap, couldn't make a ball on the break, don't even talk about spreads. I ordered a J&J Break/Jump for him. He *****ed and *****ed about it.
I coached him on how to break with it, didn't change his break spot, just moved the cue ball back a little to shorten up his stroke for better accuracy (breaks from head end rail), and now he is making 1-3 balls on the break with good spreads, which gives him the chance to get out instead of his opponent. He is breaking now as good as he did 20-30 years ago.
I have always been a hard breaker, some tell me as hard as anyone in town, but even I have noticed a little drop off the last few years, and my J&J allows me to retain the 'Snap' I have always been accustomed to, so I feel it is a useful tool as you age in the sport in order to remain competitive.
As you know, 15% is not a lot, but it's the last percentage point increase that drops that ball in the pocket, and gets a good open spread instead of a clustered one, and that IS a big difference.
And, many times, the break might decide who wins and who loses, and a phenolic tip lifts a lot better than leather for jumping.