For 20 bucks just go buy the stupid thing if you don't like it return it

1. stock build has been completely stable for me aside from the occasional lag which is usually fixed by a reboot or just waiting a minute. i thought these things would be completely unstable & crashy especially at this price but stability is actually great. lineageos is actually less stable than stock atm - it's having a temporary issue with drm which leaves most streaming apps aside from youtube completely non-functional.

2. use 5ghz instead of 2.4. if you still have issues, toggle wifi, reboot, or just wait a few minutes. i found that the issue with buffering is actually just the built in wifi card either losing or having a weak signal.

noticed that it nearly always happens when i'm opening a lot of apps quickly in a short period of time, using bluetooth or just using the box a lot in general. but just watching from a single app for a normal period of time (like a few hours) i don't get this issue at all.

3. yes, you'll have to use a micro usb otg splitter that can provide power to the device. there's some on amazon. as an alternative, you can also use a bluetooth keyboard & mouse.

4. yep, same as above. use otg & just plug in your hard drive or sd adapter or whatever like you would a pc. it's worth noting though that for some strange reason walmart didn't enable android's adoptable storage feature on it's build, so if you care about that you'll have to enable it manually. (note that the instructions on that link have you download some unnecessary app that just does what dev options do. just connect to it with adb like usual & skip to step 9)

5. yes, i sideload a lot & can confirm it's exactly the same as any other android device - either download on the device & open the apk or use adb install-multi-package to install. it's worth noting that just like other android tv devices apps without a tv icon will need an alternate launcher capable of launching phone apps.

6. yes. i use smarttubenext (another open source youtube client, made for android tv highly recommend over newpipe on tvs tbh) for hours so far & 4k60 plays just fine, never got any frame drops.

I have two of the 4k variety and intend to pick up another one. They've been rock solid for us and we've done nothing more than change the launcher and sideloaded a few apps.

We like them better than the couple of CCWGTVs that we have. Especially the remote. Hate that annoying little google remote.

Does the Onn. Android TV 4k Streaming box need a custom rom like Lineage OS to be flashed onto it for it to be reliable or should I keep it on the stock build?

No. I've never flashed anything to it. Why would people recommend it if it needed to be flashed with a custom rom to work well? There are roms for it but I haven't seen anybody flash them because they are not needed.

I also have heard reports that this device has issues with buffering so is there any way to mitigate this issue?

I've never had any buffering issues, even on Wifi and streaming 4K. I also stream 4K files directly to this box and it just works.

Does this device have mouse and keyboard support through the built in USB ports or do I have to use a USB hub to get mouse and keyboard support?

You need a USB hub.

Is it possible to add storage to this device?

Sure. Just use a hub with storage.

Is it easy to sideload apps onto this device (like downloading them through a web browser on an android phone) and if so do they usually run reliably?

Of course it is. It's easy to do that with any Android TV box.

If sideloaded apps can run reliably on this device would this device be capable enough to play 4k60FPS Youtube videos on Newpipe (open source 3rd party Youtube client) with minimal buffering?

Yes, but we tend to use SmartTubeNext instead of Newpipe since that is designed for TV.

I have one on order, so haven't worked with it yet, but did my research. Here's what I know:

1. Keep it stock, it's preloaded with Android TV 10. If you want more customizability, you can opt for a third-party launcher. In fact, I'd recommend it.
2. Have not heard this.
3. You would need an OTG dongle.
4. Same as #3. It's only $5 on Amazon: Look for Micro USB HOST OTG Nexus
5. Easy to sideload APKs. Reliability depends on the coder. Many APKs are designed for phone, NOT TV. They will work, but you'll need to install a mouse cursor app that will give you a clickable pointer that you use the D-pad and Enter button to activate.
6. Better off with SmartTube which was designed from the get-go as an Android TV app.

Google for Troypoint Walmart ONN for a starting point on what it will be like to get this device up and running.
https://troypoint.com/walmart-onn-android-tv-box/

My son uses his in college. Works great. We have the cheaper 1080p stick version for travel.

The only buffering type issue I have had with it is the Bally App, and that may be my network-wide ad blocker causing that or the app itself is just glitchy. Sometimes it stops playing or I get sound but the video is frozen. I have to pause and then catch up live to get back to it. Funny thing is that I am often slightly ahead of the Roku in my house with that same app if it doesn't have the problem. For everything else it just works better than the CCwGTV that I wound up giving my daughter when her Roku went stupid.

I really liked mine, it did run well. I had it for about a year then it started having issues losing connection to the remote, actually I had two remotes and both would stop working after 10 minutes or so. Sometimes a reboot would fix it, sometimes not.

I could use the remote phone app without issue, I think it's an issue with the bluetooth controller. I had to remove the Onn since I couldn't get it working reliably and replaced it with a Google Chromecast.

The ONN box had issues with the remote when it first came out. There was an update that fixed it. I have 2 of them and love them. Only problem I have is that on both of them HDR on certain Netflix and Prime shows is forced on. Makes the shows too dark to watch. For grins I replaced one with a Tivo Stream 4K that I had and the HDR issue was gone. But for $20 just try it.

If you run the little box for long peroids like I do being retired and all it will heat up. If I forget to turn the fan on it will heat up and I lose the Internet. But as soon as I plug the fan back in, within minutes it runs just fine.

I don’t know if anyone else experience this but I’ll throw in my two cents - my eero had WPA3 enabled. It crushed my download and upload speeds with the Onn 4K box. I went from 20mb download (thru the box) to my actual service download speed (300mb down) after I turned WPA3 off. Hope it helps someone.