This are the things i found out below which some of you might encounter as well. And some stuffs which you all can do to improve the phone..
Oneplus ColourOS
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- Good battery life from stock ROM.

- Issues with contact numbers. The rom somehow needs full +60xxx prefix if you've stored the contacts with only the mobile number and without the prefix. When u get a call it will show mobile number and not the name which is quite annoying.

- Data manager was crashing. Couldn't get it work.

- One the good side, the camera picture quality is better than CM11S. The camera also has the function called HD picture (superzoom) which current CM11S function does not have. It's ability to take 50Megapix shots is incredible.  Go google it.   I'm waiting for CM to implement this in their next version.
Oneplus CM11S
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So after using for couple of weeks.. decided to move to CM11S and see.

After installing CM11S. Some of you might encounter mobile data issues. You would get call drops whenever the mobile data is active. (3G,4G,Edge..)

To resolve this, you would need to flash the radio taken off the HTC M8 into the mobile. But for you to do that, you would need to unlock the bootloader and root as well.

Challenge was to get a proper windows ADB driver to work with the phone, I have tested many ADB drivers for windows 7 x64 and it was really hard to get the PC to detect the phone once it's in fastboot. Finally i found the needed drivers to work with the phone. Had to manually install them from device manager.

Once you've flashed the radio rome in it, it would fix this issue.

2nd step was to turn off alot of irritating features.

Do turn of Tap on wake, tap on sleep. Gesture controls. As i feel there were making the phone to wake up sometimes while in pocket or accidently trigger programs via gesture. I rather have them turned off.

3rdly.. go to the settings/privacy/privacy guard, and go to the advance setting menu.

Disable those 'keep awakes' and 'wake ups' in some of the google apps for locations. There is an issue with the google apps services trying get location data too often and also causing phone to be in an awake state too much. I've block them from waking up and keeping awakes.

4th. Enable performance &developer menu . And in performance, underclock the chip to 1495mhz.. rather than 2500mhz..
If you're playing extreme games, the chip really do heat up very very much and you can feel it in the camera at the back. And i can tell u that it really burns.. capping the max speed i feel didn't do much impact to the speed of the phone.. as it's already quite adequate for normal use.

I'm still waiting for camera to be improved. but meantime by doing the above.. the phone is awesomee.. and rock solid.. no regrets..
hopefully CM11S comes with better camera and the 50mp HD picture ability like the one they have for the OPPO 7A. since both of them using The sony imagine chips.

From the above you need to do abit of work to get the phone to work as intended and reliably.. if ur newbie, u might want to get hold of the international version and see not get the china one..

so far nearly a month.. nothing wrong with the phone.. camera and battery like is great..
I'm getting 1day 7hrs on average with the above settings and on wifi or 4G on all time.. play games, surfing facebook,whatsapp, and listening to music quite alot.