Wow. Hadn't heard of Mullvad before reading this, figured I'd give it a try. That is hands down the BEST onboarding experience for an app (let alone a VPN) I've had in I don't know how long. Took me maybe 2 minutes to go from no account to a working VPN connection. I love that everything is anonymous (down to the account credentials just being a randomly generated token).
Mullvad even gives you a 10% discount for bitcoin, bitcoin cash, and monero payments.
I am a bit disappointed that they haven't yet integrated bitcoin lightning network. That would be a huge improvement for reduced transaction fees given the low value of transactions they deal with, as well as instant confirmation rather than 6 block (~1 hour) confirmations. You could even theoretically stream nanopayments for each minute of use with lightning, rather than pay for a whole month.