I have a Xperia XZ Premium as my daily driver and I got a XA2 Ultra from Sony to review, the phone was recently launched here, in Brazil.
After three days with this phone, I would say it is pretty decent considering the price (here in Brazil it costs something like US$ 549). I has a great overall look (even better than XZP's from some angles) and a FANTASTIC frontal camera, much better than XZP's (the wide-angle one is quite bad, but the main front-facing camera, the left side mounted one, is awesome). The back camera is okay, no surprises here.
Also, the battery is really good. Using auto brightness I could get 10 hours of screen-on time (Wi-Fi only). I'll test the usage on 4G/LTE in a few days.
Besides that, the phone is uncomparable to a XZP. The performance is okay for the price, but you clearly see that it isn't a flagship. I could experience a lot of laggy animations; the phone struggles with certain apps, like facebook, chrome and some games.
Also, the screen is not as colorful, even though is quite brighter. The back mounted fingerprint reader doesn't fail as much as the XZP's, but is harder to reach. Also, the phone is even worst than the XZP when you try to use it with one hand.
I don't know. I think that what amazes me with the XZP is it's fluidity, something that's noticeable even after all these months. I also tested the Galaxy S8+ some months ago and I can say that the XZP always outruns it when it comes to speed/fluidity. I wouldnt exchange this feature for a slightly better front camera and battery on the XA2 Ultra.
Also, the XA2 Ultra's back reminds you that Sony made no effort while creating this phone. It is beautiful, but only because the absence of side bezels.