Both are Swiss zero log, Mullvad has a flat 5 euro/month charge that goes back to when they started to (they say) forever - you can send them cash in envolope for the next twenty years with a generated account number and you're away.
ProtonVPN has plans - the two year streaming sign up is 4.99 euro/month.
Realistically, all VPNs are compromised. But for most people's threat model, that's irrelevant anyways.
Proton for instance revealed the location of a climate activist leading to his arrest[2], with the inspiring message from the CEO that "privacy protections can be suspended", silently on a per-user basis at any time.
Haven't seen anything like that for Mullvad, but it's probably the same. At least the company takes crypto. But these things are always just surface level obscurity at best.
[1]: https://en.m.wikipedia.org/wiki/Crypto_AG
[2]: https://techcrunch.com/2021/09/06/protonmail-logged-ip-addre...
There is also no comparison between Crypto AG and us. Our encryption occurs client-side, our cryptographic code is open source ( https://proton.me/community/open-source ), and our tech can and has been independently verified. More about this here: https://proton.me/blog/is-protonmail-trustworthy
Finally, regarding payment in cryptocurrency, you can also pay for Proton's services in Bitcoin: https://proton.me/support/payment-options#bitcoin.
That person isn't just a climate activist, they (and others who used that email account) broke French laws. Swiss authorities compelled the disclosure.