Mail, VPN, Pass & Drive have been great for me over the past year. The lack of proper native desktop applications has been a setback for a few colleagues and is worth considering before migrating.
Hi! Note that we now have desktop apps for Proton Mail (Windows and macOS, Linux in beta, all come with integrated Proton Calendar), Proton VPN (Windows, macOS, Linux), Proton Drive (Windows and macOS), and Proton Pass (Windows, macOS in early beta).