they would snoop on the HDMI port

Most smart TVs do this by default, unfortunately. They use a technology called ACR (Automatic Content Recognition) to determine what you’re watching, essentially like Shazam but for TV shows and movies. This gets sent to the manufacturer who can then build an advertising profile about you.

At least they don’t show ads, yet.

Never connect a smart TV to the internet. Put it on a separate VLAN that doesn’t have internet access. For streaming, use something like an Nvidia Shield (or if you’re in the Apple ecosystem, an Apple TV).