> And how much "surveillance" does a VPN prevent anyway?

Changing your acc number every other month and paying anonymously is much easier on Mullvad than on the ISP level. You can also get multiple people on the number very easily. And Mullvad is likely an entity outside of your home country, hence more difficult to coerce than your ISP.

In my eyes ISPs are compromised by default so the aim is to guard against them, if Mullvad is also as compromised it's more difficult for them to track me across account numbers and, even if they do, my data is then in another country, which worries me less than it being local since I'm not important enough to warrant international action.

They aren't selling adblock. That's not the purpose of a vpn.