Along with what has already been said, for the same package deal they offer an email, a vpn, a password manager, drive, and alot more space than the competition (500gig).
they include services such as proton sentinel.
https://proton.me/blog/sentinel-high-security-program
and secure core
https://protonvpn.com/support/secure-core-vpn/
one of the few still allowing port forwarding
https://protonvpn.com/support/port-forwarding/
how to use them in high risk countries
https://protonvpn.com/blog/vpn-servers-high-risk-countries/
development over the years and their dedication to bringing privacy, security, freedom of information to the masses speaks for itself.
Encrypt the planet