Just a quick note. 3 months ago I bought the XZ Premium, because usually some Sony phones have been without PWM and caused no irritation. First I thought that this is the case with XZ Premium too. Then after using it more in the evenings, it started to cause the typical PWM irritation. I started to use it less and just thought that maybe they have now really implemented something at the driver level in Nougat, which is causing this.
I was also not able to detect any PWM with a DSLR.
Then I read the Notebookcheck.net review and learned that there IS a PWM under 33% brightness. I quickly installed an app to control the brightness so that it never goes below 34%, and bob's your uncle - no eye strain anymore!
I was hoping that they dithering or similar problem is mitigated by the 4k resolution, if there is such a problem in this device. I'm still not able to read kindle books for hours without getting a very slight eye strain, but I'm able to browse the net etc. for a couple hours a day/evening without eye strain. But I do think that if the dithering or similar that seems to be the problem in devices like Huawei Mate 9, which have much lower resolution, is mitigated here with the 4k resolution. Maybe the pixel size is just so small that any dithering is not so irritating anymore.
So might be worth a try for those who can't seem to find a device that is not causing eye strain. Just remember to keep the brightness above 33%.