Pi-hole has been excellent. I was able to discover that my Samsung TV was reporting minute by minute updates on what I was watching to a local Australian company.
Same with my Sony Android TV. That thing trying to phone god knows what home made up almost a third of all DNS requests on my home network, even with 2 adults working from home.
Since you can't buy dumb TVs anymore, you best leave the "smart" ones offline.
Worth mentioning that this is just the domain resolution, not necessarily the real volume of connections. The reason they try every second sometimes (I have devices that do exactly this, ~86000 attempts every day) is because they keep failing. Assuming they resolve once they stop flooding the Pi-hole and will bundle their connections in fewer, larger chunks. Couldn't say what's in those chunks since they're encrypted but I can make a fair guess.
But the bottom line is that the number of attempts to resolve the DNS doesn't say anything about how egregious the activity is. You could have a device try every second because it wants to send an "I'm alive" message home, or you could have a device attempt DNS resolution once per day and send all the traffic it captured from your network. Don't use that number as an indication of how evil the device is, I'm sure the most egregious malware or crappy IoT will be careful not to flood DNS requests.
Modern TVs actually reached such low prices because almost all of them are paying for production post purchase with user data. So that's generally a great idea to lock it up with pi-hole or to not even connect it at all and use an external streaming box.
I think this already made the round on HN https://phys.org/news/2019-02-tvs-cheap-smart-tv-extra.html
How does the Pi-hole achieve this? Does it have a blacklist (I assume) or can it use a whitelist? The services my TV needs to reach are easily enumerable, I pay all of them subscriptions. There is no other valid connection for it to make. Maybe firmware/app updates but I'd kinda prefer to do that myself at this point.
My smart TV remains disconnected from any network. But I use an Android TV box, so I may only be substituting one company's surveillance for another's.
Android TV is a massive improvement upon any Smart TV's UX though, so I'm winning on that count.
I'm sure you know this, but with a reasonable router you can redirect non pihole port 53 traffic back to the pihole. A relatively cheap Edgerouter lite does this for me.
Though rare to find a 4k/OLED TV that's "dumb", I managed to grab one.
If I do want certain smart features e.g. chromecast I can always just buy it individually for like $30.