Mine had EE UK firmware, I changed to Custom US firmware to try the Q preview mode.
All I can say is that it's not worth to leave 9 behind just yet. It's pretty much stock Android without Sony stuff in it, kinda miss it already, but all in all I only noticed one bug.
Connecting earphones with Jack will still have the speakers playing music, but you're fine with Bluetooth connection.
The gesture thingy is pretty weird by the way, fortunately there's the option to go to the classic three buttons.