Well, my better half purchased a Z last week. It is still running on 4.1.2, and after seeing the differences in the UI, she leaning on the idea of not updating to 4.3. An update to 4.2.2 might be where it stops. 4.3's update brings about UI changes which are a serious setback of design and functionality.. It give the UI a crude and unrefined look, the settings panel which was a nice and contrasted white font on black background is now a bland black font on white, the alarm clock styles are gone.
The app drawer is somewhat better, but it's the only welcome change. Other than that, it's just a blander UI with more bloatware added by both Sony and Google. In my case, if I could go back to 4.2.2, I would, in a heartbeat.