I couldn't pass up a 10% discount (Best Buy Movers coupon picked up from the post office) on this and just picked this set up myself. I was considering the Samsung JS9500 or waiting for the KS9500 but then saw this come out of no where and took the plunge.
My short version review is the picture quality is great, no complaints there. I wouldn't count on using the tablet/smart cast feature without experiencing some frustration. I have never used a TV's native apps in the past but I gave this one a try with the new tablet/smartcast design. Atm you are better off using an external device to provide the content IMO.
My long review:
This is one of the few TVs that are supporting the Dolby Vision HDR format. Netflix is starting to provide this content. Macro Polo is one that is well done. When watching Marco Polo it looked great. From the start you can pick out so much detail like the embroidery on the robes etc. When watching it I did notice some weird artifacting issues now and then. It's hard to say if this is the fault of the source or the TV's interpretation of the source. The most common scenario for this is on a scene with a bright sky with a lot of dark horses/shadowed faces on the bottom. The beard of the main focus will get what appears to be groupings of stuck on pixels. Its somewhat rare and not terribly distracting. (This is using settings similar to the OP Calibrated Dark).
I expectrf some roughness as an early adopter but right now it is to the point where I would not recommend the TV to anyone except a patient enthusiast willing to have to spend a significant amount of tinkering if they aren't using an external source for their content.
The set came from firmware 1.0.0.0 so understandably I needed to upgrade. In order to play Netflix it said I needed to upgrade. The instructions on the screen asked me to link to the TV but unlike the initial setup it would link. It said otherwise power off the set and let it update. I power off the TV and wait 30 min. After powering it back on there wasn't an update message but Netflix no longer gave the error that I needed to upgrade. However casting still did not work. It would get to the Ready to Cast screen but never start when trying to play but it would not start. I then downloaded the latest firmware and used that to upgrade. I was then able to get a little further but Netflix casting was still having issues. It would start playing and I would get audio but no sound. Pausing from the tablet would show the progress bar but no picture. I skipping to the end and it showed the 'starting in 30 seconds message' with just the border around where the image for the title should be. After a full power off by disconnecting the TV (using the power button on the back of the TV seems like a soft power off) I was able to start casting successfully. However I still have constant issues where sometimes when I start to cast I get audio but no video. When it gets into this state I have to restart the TV. This is something that software updates can probably fix but for now other family members using the TV call to me to get it working again. Youtube has a stuttering issue. Also switching to a different youtube video and trying to cast it while a video is already playing reslts in the first video being re-casted instead of the newly chosen video. Also software issues that can be worked through. These aren't rare edge case scenarios that made it past QA though...
My next issue is the quality of the network adapters themselves. At same location as the TV, the tablet completes a speedtest consistently with 120+Mbps (5x the recommended to stream HD) However while using the TV with WiFi at 75-80% signal strength I would constantly see Netflix streaming and go to loading, and it would stay in 480p/1080p and not reach 4k (Marco Polo/Daredevil) I tried 2.4g and 5g connections with the same results. This looks like a hardware issue that can't be resolved. It looks like they chose a cheap wifi/soc solution. As a comparison I have a PS4 and a recent but cheap model Sony BR player with Wifi at the same location. The PS4 streams w/o issues (gamers wouldn't put up with bad network connectivity) however the cheap Sony player does not operate as well. I switched to a wired connection to the TV and I started getting 4K streams within 5 seconds of starting (my internet connection gets 300Mbps results from speedtest ) Unfortunately the NIC for the P75 is a 100Mbps card which is a disappointment and doesn't seem good from a long term future proof perspective but for now it is sufficient.
I like the direction of the tablet/casting methodology to control the TV. I think this TV was rushed to market when much more testing and refinement is needed in this aspect. I expect some device combinations to have issues. I couldn't expect them to account for every device out there. But these are core features with the provided hardware that aren't functioning properly. For the average user the TV is going to be a frustrating experience as they try to work through these issues. This is the direction they are going with all of their TVs though so I'm sure their engineers are focused on improving it.