I'm seriously considering it, but I'm a heavy IMAP user. When you enable IMAP in ProtonMail, it's no different than any other mail provider, security wise.
Other people have made good points. Just wanted to add: you'll feel better knowing you're no longer vulnerable to Google. It's a nice feeling of relief knowing Google could cancel my account tomorrow and I wouldn't be hurt in any substantial way. Definitely worth the effort to move your email to an independent provider.
Technically no different but you have cast a small vote to behavior you no loner tolerate or support (socially). Even if it’s a fraction of a dollar. In aggregate they add up.
AFAIK you bypass 2FA when you use IMAP. I don't see many advantages of using Proton (over any other independent e-mail provider) without 2FA.
The thing is, I connect all my accounts to a single mail application and handle everything from there, including their automated backups for ~15 years or so.
It is for this reason I am moving away from ProtonMail to Migadu. Literally any IMAP-offering email service would do. All that we need is a custom domain.