This update has a lot of bug fixes. Some are in Wifi and some in Bluetooth. There is 39 security fixes too. You can find a full list here. I suggest a good image backup before you update – I use SuperDuper for this.
- 12/14/15 – added link to SuperDuper. Very nice tool!
- 12/9/15 – one MacBook Pro (Retina) updated without issue.
I will let you know how my updates go.