I'm glad I never did. I looked into proton a few months back and was highly suspicious of their non-profit status. I could never put my finger on why but felt off.
Do you happen to know any alternatives for their email? Some security guy on YouTube was talking about how their email aliasing is better because if you lose a single email/password combo, you're not subject to any other breaches.
I mean I already use a password manager since I adopted KeePass like 15 years ago and use Bitwarden now, but I still like that concept.
Depends on if anyone you message uses proton. If they do, you can always get their pgp key and save it to thunderbird. If nobody you know uses proton, there is no benefit to their service over the above.