>Mullvad is rather principled on privacy. You can't even make a real account, you can only generate an account number that you can charge, and I assume they do some sort of clever tricks to keep themselves as blind as possible to who uses the account number. Firefox Relay is also just whitelabeled Mullvad, so they have Mozilla's stamp of approval.

Yep. And I use the VPN connection (and/or TOR) to re-up my Mullvad VPN when I run low.

Mostly I use the VPN to protect my privacy when posting with a throwaway account here and/or other sites. And of course for torrenting.

What's more, I had some monero (XMR) left over from some other transactions, so I use that to pay for the VPN connection.

As such, unless Mullvad is storing the IP address from which I connect (and they claim they do not), it would be difficult (but not impossible -- I don't always use VPN when posting anonymously/throwaway -- that isn't a challenge!) to identify me through my VPN connections.