Firstly, this project is open source. If you suspicious of where the data is being stored or my intentions, you are free to fork and run it yourself.
That being said.. I am not claiming to have achieved some novel security accomplishment. Yes, this is a simple symmetric encryption using a vetted crypto lib, backed by a key value store, and using UUID4 to generate the links.
Its a trade of for convenience and security. It's better than emailing passwords in plaintext and makes security more accessible to folks who dont have the time/incinlination/technical ability to set up keybase and/or estbalish PKI for sharing secrets.
Understand the audience this is targeting..