for DIY better buy from this SITE...im repaired my xoom,sensation and my nexus 7(2012) by myself...
this site sell so much cheaper than others'

alright, decided to go for the L1520 already 
Is it necessary to flash this device ?

same as mine...
seems like denim update got bug with it

try double check the battery sense if there is any new apps started to run on background after the update?

so weird?

Mine can rotate fine even with location on, just that it takes like 3 - 5 seconds to detect
Yes, I think all Lumia 1520, 930, Icon users have this issue. I noticed this right after installing Denim. There's kind of a fix if you not willing to try phone full reset, which some ppl have said fixes the issue. I'm definitely not going to full reset my phone. With the latest update of Lumia Camera, I found that letting it stay in the task manager fixes the gyro issue. But this doesn't fix it 100% of the time or is it instant. I just leave it at the task manager, wait 10 mins then I find my gyro working pretty much like normal. If all fails, restart your phone. 

Lumia camera will go background if u press the back button also. Just keep it there, don't go task manager close it on purpose.

My experience here in Kota Kinabalu is bring receipt & phone. Phone will definitely not come back looking pristine lah, maybe slight tool marks. Only issue is how long usually have to wait for them to fix the phone. This was my experience with my old Lumia 920
Ah ok, really have to factory reset the phone to fix it permanently. Great. Anyway since your phone just reset, insider pro won't be able to give correct battery life estimation. Usually this takes a week or 2 after u settle down with all the apps configured & background tasks running.