Had a punt to see how it works.
Nice, all it does is adds a line to the copyright page, fully visible - didn't even try to hide it (Its basicaly a encrpted string, I assume if you know the encryption key it will give them your username.
Well, a type of DRM I have no problem with at all, fully editable in Sigil and the pirates can take about 20 seconds to remove the paragraph, still it should discourage casual sharing over facebook etc as it's easy to track if not removed - so I'd give it a win for the stated purpose of DRM
The Exif info on the image has a strange description as well (so probably linked to your account), And If I were them I would have embedded some info in the pixels as well.
Formatting looks good.