I have installed via USB and tested Block This (open source) and Adguard (not together. One per time) on my KD49XD8099 with Android 6.0.1 and they simply worked great! No more annoying ads (yes, I know. Companies don't like it, especially Google, but they are perfectly legal. Also we are allowed by Android itself to install whatever we like).

The only problem is that after turning the TV off (standby) few hours, when I turn it on the television starts rebooting. Uninstalling them the television (and rebooting just in case) Android becomes "stable" again (quoted because I've got reboots even without tampering with special apps). The apps were set to enable the VPN at boot. Not that it should matter, since the reboot happens just putting the tv in standby.

Now, I do understand that an external app, not made specifically for Android TV may not work (but as I wrote they actually do the job they are made for), but if the television/Android reboots there is a (very critical) issue with the OS, not the app. To test the issue the developers just need to install the apps mentioned (again, enabling the VPN at boot).