This is not really an 'email service' the average person can be expected to use..

That's not SMTP or other industry standard protocol, incompatible with any mail client out there (?) -- it's for sending mail from backend services, not using as personal email.

Even if you make it work with some SMTP adapter, you still need external mail server as on reception side Cloudflare don't provide storage/IMAP service, only route/redirect mail.

I use it (routing to Gmail, Mailgun SMTP for sending) and it works. But it's not really a mail service if it depends on some another mail service to work.