Even without all the capabilities of protonmail(yet) it's interesting the fact that they've managed to allow encryption communication without having you to create a new account...
How's it a worse version of PGP? It's similar in that it uses asymmetric encryption, but it has the benefit of having the private key stored on an HSM.
How are these certs handled by other mail clients/systems? Do they have a chain to a widely accepted Root CA?