After a few days of use in 10 II (Dual SIM) I would say that 4.1 was operating more smoothly. Battery life is significantly reduced, loosing 40% overnight and phone barely lasts 24hrs (before it would easily survive 2 days). The text prediction as other mentioned takes for ever and freezes the phone once you select a word from the proposed ones. When on WiFi most of the Android apps think that there’s no internet connection. When walking outside the house, the phone keeps looking for the WiFi instead of switching to mobile data.
After flashing I had to do several reboots to get things working and at least once the phone was stuck with green LED on and no way to light up the screen. Exchange didn’t sync until after serveral reboots.