This is neat, and the I really like the UI too.
I made something similar (except the one-time view part) not too long ago just to experiment with storing the base64 encoded message into the URL. It also has an option to add a key, which uses a javascript implementation of blowfish.
Since the message is stored within the URL, there's no backend needed, though that means the message needs to be short since most modern browsers can only support up to about 2000 characters in the URL and the messages can generate a long base64 string rather quickly.