That is the least bad thing they could do btw. Unless your internet is data restricted, go for it if you want free cable. If questioned by your ISP (extremely unlikely but theoretically possible) pretend you have no idea what they're talking about.

Firewall it from your local network if you want to - it'll still work - they're not after that.

Absolutely, and this is why I refuse to run connected devices on my network that do run software I can reasonably trust. This is also why every computer, phone or appliance I own runs Linux. This includes my TV box, which I recently migrated to an x86 port of Android with Claude's help.