I might be able to assist here, my last phone was an Xperia Z3...great phone that I was initially very happy with, however after a few weeks cracking appeared in the rear glass panel near the camera which was disappointing given the main reason I purchased it was for the watertightness. I might add that I didn't have the phone in a case for those first few weeks, however the phone was never dropped. Rear panel was replaced and phone was sealed in a nice Spigen Ultra Hybrid case....all was going well for about a month when more cracks appeared on the replacement rear panel (again the phone was not dropped or subjected to any force. At that point I started looking for a phone that didn't use glass as the primary component for the structure of the phone hence the Nexus 6P was the obvious choice. So far so good (no cracks as yet) an it hasn't bend in two like certain videos would have you believe. As a side, despite the Z3 and 6P sharing Sony camera sensors (albeit 20MP versus 12MP) the Nexus actually takes a better photo...not sure if the Z3 and Z5 sensors are the same.