Finally upgraded my parents’ two C4 Dual. They’re now more smooth ( at least no more lag while doing the same processes) . Also seems longer battery life ( I tested play the same several video files and watch the same YouTube videos via wifi) .
It is amazing that the camera shutter delay now is shorter, means respond faster. However, photo saving to microSD takes longer. Also, the photos taken by 6.0 are more sharp ( could be due to shorten the shutter delay) and more vivid. Now, the colours of photo and the real looks the same. When 5.0, most photos look a bit grey.
Thanks to SONY