The best thing about proton mail was that it has an option to send messages offline which helps me in my daily work as well as when I am traveling or out for some reason there are no internet connection available. It also provides end-to-end encryption so i can be sure all data transmitted between us will remain safe from prying eyes if needed. There could have been more features but those were not really much important because its free service with good security measures included. So far nothing bad at this point. But then again I haven't used too many other services like google drive etc. This one just gives you peace of mind knowing everything sent through them remains private & secure until read by recipient only.