[Philips, Sony, TCL Android TV] jFalner:
My Bravia X700D never had any major problems with the menus, but the upgrade to Oreo definitely fixed the volume adjustment flakiness. Now it is quite speedy, except for immediately after boot while everything is getting loaded into memory. I've found that a lot of the bloatware can be disabled in the Settings and notifications turned off. This gives you a wee bit more performance. But the holy grail is having root access—as far as I know, there is still no safe and reliable method for root on a Bravia.

Untrusted sources is allowed, as long as your television is in Developer mode. To get there, go into your Settings and find where your Android version is listed. (For mine, it's Settings > About > Build.) Highlight the Android build information, and start clicking the action button on your remote. After a certain number of presses, you'll get a notification saying you are now a developer. This opens up a Developer menu in the Settings where Untrusted Sources can be enabled. Of course, make darned sure you know where you're getting your stuff from!

Once Untrusted Sources is enabled, you can sideload pretty much anything. I've got Mozilla Firefox for Android installed, using the APK available from Mozilla's site. Works beautifully (including using uBlock Origin to block all the YouTube annoyances and ads). But there is a drawback—sideloading means you don't get automatic updates from the Google Play store. When a new version of a sideloaded app comes out, you'll have to update it manually.

Some apps incorrectly guess the orientation of the Bravia or assume portrait, so you might see certain apps turned sideways on the television. (I know the Weather Channel app does this, and I'm sure there are others.) There are apps on Google Play which can override the orientation for all apps, and you might need to sideload one and force all apps to landscape.

You'll find that any Bravia is quite capable of handling high profile video and large bitrates. I play NAS files over both Ethernet and WiFi in my house, and both work equally well. Any bottlenecks will almost assuredly be with the networking, not with your Bravia's CPU/GPU. Kodi is also pretty lightweight on a Bravia—I can play from Internet, NAS, and Flash/SSD storage attached directly to my Bravia quite nicely. (Internet is the weak point here—if a remote server can't push it fast enough, you can't play it smoothly. Thankfully, most Kodi addons allow you to download video sources, and playing a downloaded source is smooth and worry-free.)

One thing I would give consideration to, however—Sony televisions are awesome, but the Android-based system software is terrible. If you have the technical prowess, you might find more satisfaction in a lower-cost Sony television which isn't "smart" partnered with a device like a Raspberry Pi. You can create an Android environment on the Pi (or Windows or Linux, whatever makes you happy) and load it up with exactly what you want your television to do. Kodi, your choice of Web browser, an FTP server, remote desktop, gaming emulators, whatever you want your television to do. The Bravia can almost double as a computer, but it was never intended to be one. So consider carefully what you want to do on your TV before you decide how much to spend on it. As for me, I went with the full Android smart TV model, and for the most part, I've been pleased as punch with it.

Best of luck!

jF