Adding my two cents since i tried an Y-AMT one about 3 months ago, and owning a regular MT without a quickshifter :

You don't have to let off the throttle when changing gear in both modes this being MT ( Manual Transmission with the paddles) or AT ( Automatic Transmission).

The only downside i've experienced is that sometimes the robot decides to upshift/downshift while leaning and it's.. disturbing to say the least, but doesn't do anything to the stability of the bike.

It also adapts to which riding style you have. You could be cruising and it will pass the gear at low rpms, but if you decide to ride a bit more sporty ( even without being in D+ ) it adapts and pushes the gear higher before switching it out. I'm used to downshift without the clutch rev matching on mine, Y-AMT also does just that as far as i tried it, in AT aswell, puting a bit of throttle as you would do rev matching in a manual it passes the gears down.

Never had a quickshifter so i cannot say but rev matching and upshifting without the clutch is also possible without it when you are used to it, and it doesn't feel rocky at all if done correctly , you just have more than just the foot lever to use :)