They don’t require an account (username/password) for you to use. You pay them for an account number and use Mullvad VPN by inputting it.
They were about to be raided but they managed to get out of that with their lawyers.
It’s also very easy to use on Linux because there’s a GUI, which is great. CLI seems overkill for an app that needs to be turned on and off (i.e. NordVPNJ my old VPN).