Like any automated manual, the i-Shift damps the throttle on upchanges to prevent damage to the lower gears. Unfortunately, when this happens, some drivers try to compensate by pressing the accelerator harder, and this is what leads to the uncomfortable lurching effect. For smooth progress you need to feel for the changes and lift slightly as they occur, or simply take it very gently. For maximum acceleration yes, you have to switch to manual and use the paddles.