Here is my feedback on this product:
The firmware is pretty buggy. I am currently in 0.66. With my Panasonic, I couldn't launch Dovi movies, then go find out why by just touching the brightness, contrast settings and going back to HT4 and relaunching the Dovi file where it can read the Dovi. It was a bit chaotic at first (suddenly yes, suddenly no), and almost all the time Films in Dovi play. The image is beautiful I finally enjoy it. Some slowdowns on some Bluray UHD Dovi, but not enough to whip a cat.
On the other hand, the Dovi x265 encodes (lords of the rings, Hobbit, Total recall) pass nickel chrome, the image is magnificent. I don't have any stuttering worries since I only watch FR tracks, and for the atmosphere for me I have more worries by remuxing them in THD + AC3. So I'm no longer expressly in a hurry to have new Firmware (hoping that it continues to work). Namely that I do not use the VS10 engine but am in a car. And you can clearly see the difference on some Movies between playing it in HDR and in Dovi, I suppose it's because the Dovi was better integrated on some than others, like when the 4k came out, at the beginning the master was only upscale.
So after a difficult start the Z9x is suitable for my use. But I cannot explain the why and how of this erratic functioning which improves on its own. I even wondered if the processor has a learning AI unit.