I am in need of a new mouse. Yesterday I went to my local Apple store and picked up a new Magic Mouse 2. It looks almost identical to my previous apple mouse. The big exception is the built in rechargeable battery ( a really nice feature ) and the fact that it only works with OS X 10.11 El Capitan.
I spent some time on the Apple website and confirmed this. The bad news is the older version of the mouse is now hard to find. My local Best Buy and Apple stores no longer have it and won't/can't order it.
The Apple store suggestion is just update the OS on your computer and the mouse will work just fine. Not something I want to do just so I can get my new mouse to work.
So in short, be warned about the new magic mouse 2... It wants El Capitan...