A little bit of luxury :-)

Granted, this part is not cheap. But the Magic Mouse is not available in a real battery eater and sometime my battery replacements was too annoying.
My first impression: the device is very valuable. Design and manufacturing make it a piece of "worthy" Apple accessories.
The USB cable might be a little longer, because you can the part so only right below the USB ports or - as apparently foreseen by the form factor ago - sit centrally on the stand of the iMac. For a left-handed placement would be on the left side but cheaper. The part invites the way through the USB port on your iMac, and even when the iMac is in sleep mode. A separate power supply is not there.
During operation, it is striking that the base plate would be better a little harder, because the mouse from the bottom plate is magnetically attracted and thus the bottom plate in resuming the mouse from slipping regularly. But is picky, but even no points deduction.
Overall, a reasonable part, an eye-catcher - and one less problem.