So, I used to work for Sony, and probably shouldn't write about them here, but heck, I'm sure Dave won't sell me out.
So, looking at the Sony products from the inside...
The electronics and antennas in them are second to none. I have nothing bad to say about that at all.
The software has become pretty good now (much better than the Ray for example). There's minimum bloat and customizations. And the few that are there, I actually miss now that I've switched to a Nexus device. And I'm not someone that enjoyed drinking the corporate cool-aid..
In fact, my Nexus 5 is a lot less stable than the Z-series I had last at Sony. And that wasn't even running the final software..
If you look around the internets, you'll find a bunch of belly-aching about getting the latest Android updates in a timely manner. Now, I could explain why (Sony dancing too much to the carriers pipes, and the carriers dragging their feet), but in the end, yes, you will get the latest Android a little later on Sony devices. But it's definitely finished by the time you get it.
Now, for the really bad stuff, and why I doubt Dave should get one (unless he's upgrading his wifes Compact Zx), and it's the mechanical part of the phone.
The water-proofing is an excellent idea, and it works. It's so nice to not having to think twice before taking your phone out if it's raining. You can bring it to the beach and go out in the water with it to take pictures of the kids (your own, not other peoples kids..).
However, they are _very_, _very_ fragile. I've broken more screens and backs of the Z-devices than I can count, and I'm generally quite careful with my devices.
Dave, being the active and energized guy he is, would probably break it in the first week..
Whoever at Sony that came to the conclusion that a glass sandwich was a durable mechanical design should probably buy a return-ticket to planet earth.
Oh, and battery life is excellent. Just make sure you enable "Stamina Mode", and only make exceptions for the apps you really want notifications from. It makes a world of a difference.