I commented on the G+ Forums in regards to issues with updating Android versions.
This is only my opinion and experience.
I have noticed some devices when updated to the latest Android version lose a feature and at times gain a bug. From my experience going back to the My Touch 4G with Ice Cream Sandwhich when it updated to #Gingerbread it lost the all in one feature from native Android contacts having the ability to assign ringtones, notifications, breathable Led lights and wallpaper to individualize who was calling or texting you. When I finally upgraded to LG L70 on early Kit Kat4.0 when it updated to later #KitKat4.2.0 it lost its zing and some wonkiness occurred with the SDCard and OS, it ran laggy and overheating like crazy. I then upgraded to Ulefone Be Pro which was advertised as #Android5.0 #Lollipop but when I got it, it was KitKat4.4.4 which ran perfect with all features like Hot Knox and Mira Vision. When Lolipop was rolled out we lost both those features as well as hifi-sound and camera quality. I since reverted that phone back to Kit Kat 4.4.4 and have all the features back. Which brings me to Axon Pro, Lollipop 5.1.1 was solid and the upgrade to Marshmallow 6.0.1 made it, for some like myself better, but for others their experiences vary and quirks have been reported. The main thing we have to keep in mind, is that no Android version is without its difficulties, we just have to either accept an upgrade may have quirks and adapt or not upgrade.