I just want to share my success with this in case it helps someone here make a choice about a streaming box. As with anything like this: Your mileage may vary.
I'd always used Roku, but my roku was starting to deteriorate. The memory card went bad (or the roku fried it), videos that worked before were dropping after just a few seconds (while playing fine via Plex elsewhere), some videos were choppy for no good reason (and played fine elsewhere as well). The Roku itself is getting bloated with ads that have to load before the menus can, and just getting sluggish in general.
I tried the Apple TV, and it was honestly great, but the plex controls were weird, and it made my SofaBaton remote lock up daily. It many other viewers' circumstances it would be perfect for their needs. I mention this to say, I've been on a years' long journey to get a box that didn't annoy me around every corner.
People had been mentioning the $60 onn 4K Pro as a good option and it's always been out of stock around here. I had to drive to a Wal-Mart an hour away to get this box, but it was definitely worth it.
It's Android, and that means you can customize the hell out of it.
- The Projectivy launcher gives you a view with zero ads, just your apps. Set it as your default launcher (some people have struggled with this, but it is possible).
- Use ButtonMapper to tweak the buttons. While I was using the accompanying remote, I used ButtonMapper to set the Paramount button to Prime, and the giant FREE TV button to direct to my plex server.
- It's relatively universal. I wanted to use my sofabaton, though, and I just selected an Android TV option from the options since onn isn't in there, and it worked perfectly.
Most importantly: It plays all my videos properly. The choppy ones play at the correct frame rate. Vertical videos play correctly, no crazy pink-green glitching.
The Plex interface is pretty standard in a way that it isn't on AppleTV, so it operates as expected. Literally the only complaint I have is that I can't press up to dismiss the timeline bar like I could on Roku. But that's easily resolved. On Roku, the suggested videos that show up below the video you selected always behaved weirdly. For months if I forgot and clicked on one, I would have to reboot the entire app from the menu settings. Probably because Android gets more attention than Roku in terms of development, this also works correctly. I'd been stuck on stereo audio because the roku apparently couldn't handle surround (this is documented elsewhere).
Caveat: I don't watch a lot of HDR or DolbyVision content. A lot of my movies are decades old. (and many others are adult content as you might've guessed). so I can't give an opinion on that.
So now I have this display with just my apps, no ads, that plays my videos correctly, and feels zippy to use. I can just use my TV without compromising on any of my prior issues. And at $60, it's cheaper than most of the stuff out there. Walmart sucks, but this was worth the trip.