Wow very interesting!
Can you explain me how does it work?
Thank you Alan.
Its basically an offline client for ethereum running inside the browser.
This means, all cryptographic operations like signing etc. are done locally on your computer.
Something is stored on the server though and that is an encrypted version of your wallet.
This again means that nobody has access to your wallet but you.
Once you log in the encrypted wallet is downloaded by your browser and decryped locally using your password. Then the client is run locally and allows you to send and receive funds. Just make sure you use a strong password, its hashed 5000 times though so bruteforcing it is not possble.
You secrets never leave your computer which makes the wallet as safe as a local GETH client.
Also you always own the private key. So you at any time can import it into your GETH client and continue using your wallet entirely offline.