Re: STOP THIS AT ONCE!
I shall resist owning one of those
Good luck with that - if you want a larger screen size with a decent picture quality you're likely to be out of luck. The reason the "dumb" ones are cheaper is that they strip out everything - including the more expensive panels and advanced video processing.
I also suspect (though I have no actual knowledge) that the cost of "smart" TVs is to some extent subsidised (or the margin is maintained) by the potential to upsell commercial streaming services and/or user behavioural data, so the incentive to sell dumb devices is diminishing.