Hi. I've been on JB_WW for the longest time cause I think it's quite stable. But recently I'm having very weird battery problems. So I thought instead of doing a factory reset, I'd just update firmware. Reading this thread, still not sure of the 11.2.5.26_WW. Should I update? Any weird bugs other than the laggy issues due to the underclock. Thank you in advance for any inputs. Really appreciate it.
Similar to you, I was on JellyBean for a very long time, resisting the switch to KitKat mainly due to reports of multiple bugs and particularly random reboots. This is an unacceptable fatal flaw as it makes the device not fit for purpose.
I made the switch to KitKat 11.2.5.26_WW when the random reboot flaw was fixed, and I needed KitKat to run AutoInput for Tasker app. In docked / tablet mode, the tablet built-in microphone did not work on phone calls. This fatal flaw has been fixed with the KitKat 11.2.5.30_WW OTA update. Personally, I also noticed bluetooth connectivity improved in KitKat (e.g. I no longer had to turn bluetooth off/on in order to get devices to connect or reconnect). Battery life is not the New Padfone Inifinity A86's strongest point, but I have my phone docked in tablet mode most of the time when I'm not out and about.
However, one fatal flaw remains unfixed and it has to do with docking / undocking the NPFI to / from the PadStation. After docking (i.e. in tablet mode), the physical volume buttons stop working (completely unresponsive). The softkeys (Back, Home, Recent Apps) still work. After undocking (i.e. in phone mode), the physical volume buttons stop working (completely unresponsive). The softkeys (Back, Home, Recent Apps) will still vibrate when pressed but will not perform any software action (e.g. once I go into an app, I'll be stuck inside the app with no ability to go Back or Home or select another recent app). This fatal flaw is always consistent and reproducible. The only way I have found to temporarily deal with this incredible annoyance, is to reboot the tablet when I dock the phone, and reboot the phone when I undock it from the tablet. It is another fundamentally unacceptable fatal flaw which makes the expensive flagship device not fit for purpose. I suspect there would be quite a number of NPFI owners out there suffering this flaw in silence.
I have many ASUS devices, and really want to continue to support ASUS. But like many other frustrated NPFI owners, I am waiting perpetually for ASUS to shape up and deliver Android L / Lollipop, hopefully to fix fatal flaws and various bugs. After promising NPFI A86 customers that it would be delivered in June 2015, ASUS in May 2015 gave a bemusing excuse suggesting "limitations of NPFI's CPU" to cancel this critical software update. No doubt ASUS faced the wrath of not-so-naive customers and thankfully appears to have done a backflip (ASUS now suggesting Q3 2015 for Android L update): http://www.asus.com/zentalk/tw/forum.php?mod=viewthread&tid=82378&extra=page=1
If you only use the phone (no PadStation), then you could probably update to KitKat without too much fuss. Otherwise, I'd suggest staying with JellyBean until the Lollipop update.