I play with a Z2, switched about 2 years ago from my stock shaft, I really went with the Z2 because it was closer in diameter to my old shafts (which were about 12.1), and having played a lot of 3-cushion I liked the stiffer taper as well.
There is definitely less deflection than a normal stock shaft, and I can shoot certain types of shots with no allowances at all, but maybe that's because the minimal deflection and minimal swerve cancel out.
Several players in my room swear that the Z2 is "hard to control", they feel with a standard 12.5 or 12.75 shaft they can hit center better. They also say or think that the Z2 puts a lot more spin on the ball.
In my opinion, the smaller tip does give you the feeling that you have more pinpoint position, but ultimately only a small portion of the tip actually comes in contact with the cue ball, and I don't think that portion is that much different (if at all) with a smaller shaft. It's more perception I think. And as far as spin, I can put a lot of spin on the ball, and I didn't find it got any better necessarily with the Z2. I can grab a 314-2, or my old stock shaft, and draw the ball just as far or spin it just as much, I think it's more stroke or tip dependent than anything particular to the shaft. Maybe for beginning or intermediate players something like the Z2 would put more spin on the ball because they end up hitting more to the outside edges of the cue ball (or feel more comfortable doing so), or maybe the smaller amount of deflection gives them confidence to use more spin.
Either way, the Z2 and comparable shafts (OB2 etc.) are great shafts, and if you like them and play well with them then by all means go for it!
Scott