The top of the mouse is covered with a multi-touch area, so it has no additional button. Scrool, two-finger swipe, click, zoom, double click is easier if you can do it on the same sourface.
Magic Mouse uses powerful laser tracking that’s far more sensitive and responsive on more surfaces than traditional optical tracking, and it connects wirelessly to your Mac via Bluetooth.
Even when it’s on, Magic Mouse manages power efficiently, by detecting periods of inactivity automatically.