The key is to verify that the TV will return to just showing "HDMI 1" or whatever after power off.

Because the smart TVs have a history of returning to whatever ads they want to show after power on.

My particular TV, if it's never been connected to the internet, will not show any ads. It will show a notification that it isn't connected to the internet when you turn it on, but it will work fine otherwise. It'll even switch to the correct video input if you power it on through that port, say through a firetv stick. Otherwise, there's a setting for power on behaviour: 1. go to home screen 2. Go to last used input.

Even better, if you can avoid accepting the ToS for the apps, they don't even start. My Samsung TV is so snappy now because I reset it and ignore the accept ToS button :)

Makes sense.

Telemetry takes packets out of your bandwidth.

These boxes have constant calls so… yeah free that space up

This is step beyond that, none of the crappy Tizen apps or anything start at all. The TV never gets network access of course :)

The FireTV is not an actual television set. It's the "something else" that you use to stream content to a screen with no internet connection.

No, in this case it is actually a full size TV that has the same OS as the FireTV stick.

My bad, I only quickly skimmed TFA, didn't think these were actual TVs since they're not available where I live last time I checked.