The Magic Mouse would be great if you could charge it using your iMacs USB port like if the mouse had an internal battery and lightning dock.
As it stands its useless as it eats about 50% of its battery power in a days heavy use.
I hope not. The point of a wireless mouse is to be wireless. 50% in a day's heavy use? Get an Apple battery charger. Apple's rechargeable AAs are great and last me about a couple of weeks under heavy use.