Completely free as in you don't have to give them money.
But you need to give personal information which also has value.
But you need to give personal information which also has value.
At most they could see domains, ip addresses, timestamps, and http-only sites (are there any left?)
But the person sitting next to you can see everything.
Privacy filters are a thing.
they are essentially looking head on at it.
that may work for business class, but not economy.
privacy filters aren't magic.
You also give up your personal information when you step outside, take a bus, train, or drive a car.
Hell, even if you stay at home, you are giving up information for free that you are NOT outside.