I have very short device history.
lumia 820(1week) -> lumia 820(2,5years and still going) -> lumia 640XL(2 weeks) -> lumia 640XL(arrives tomorrow).
I used 820 for a week then rebecause i got damaged unit. It couldnt awake from sleep and it was restarting itself randomly.sent device back , got refund and bought a new 820 again

after 2.5 years i decided to buy a 640XL with cracked glass , replace glass and use it. Then i failed. Cracked LCD completely. Bough new LCD and i founded out new screen was faulty either. got refund for broken screen and sold device (bye

) . 3 days ago , i bought an used 5months old 640xl and still waiting it to arrive. I'm living in very weird country so thats why i cant buy unused/brand-new device.price of unused 640XL is 270USD . dont even ask price of high-end devices like elite x3 (1000-1200 USD).