I've been using Proton as an alternative to Gmail. Potential security issues aside it's been ok. Web interface is definitely more usable than Gmail is now. Big down side so far is no SMTP/IMAP support on the free plan. You need a paid plan to use a real email client. Caveat emptor.

In order to perform encryption and decryption in your web browser and to properly authenticate you, we need to use JavaScript for the encryption and decryption process.

As any legally operating company, we need to comply with the local legislation. However, do to the zero-access encryption we use on our servers, there is very limited data we can provide in case of a data request. Particularly, we cannot share any of the email content (including attachments, content of your calendars, password, files stored on Proton Drive) in an unencrypted form, because we have no access to those ourselves.