I wanted to de-Google, and initially I was using Kolab Now for about two years, and that was terrible, so I was looking for something to replace it, and someone told me about Proton. I have custom domains mapped to it, so if they piss me off enough I could migrate to another service easily enough.
I like having slightly increased security, but I'm not delusional: if I were doing something that I was worried about the government seeing, I probably wouldn't trust any cloud service blindly.
I got in early enough to where they gave me a boatload of storage, a bit more than a terabyte, so that's kind of nice to have as a backup for my photos and the like.
(And, BTW, if you are involved in Al-Qaeda, i.e. if you are really truly concerned about anyone reading your emails, it's not like you can just rely on Proton and relax. Both because your recipients likely don't use Proton, and also because the more serious you are about such concerns, the more emphasis is on that "allegedly" word. So I'm still not sure what I'm buying.)