[olkid]

short answer: no, it's not secure

longer answer: look at the last script tag in the demo page, it exposes the encrypted HMAC string, the encrypted HTML text, the encryption method and even the library used to decrypt. You can easily brute force the passphrase

...or better yet embed some code in a popular web page and have the netizens brute force it for you (distributed computing).

In general, client side obfuscation is difficult to perform securely as it shares too much information to be secure.