When I used GPGMail, I didn't mind giving them a few dollars to support it. It's nice to not have to, though.
can affirm that gpgtools + mail.app is close to seamless, once the keys are already exchanged.
But only if it works with your OS version. It always takes them a few months to support the update. I'm not complaining. It's not like they're a giant company making megabucks to support it. But if you buy a new Mac today with Sonoma pre-installed, you're gonna have to wait a while before you can encrypt your email.