I consider that a feature that they continually update the image with bug fixes and new anonymity-enhancing features like obfsproxy bridge support and stream isolation, along with updates to TorBrowser, which itself is heavily fortified against privacy leaks. Liberte hasn't been updated in almost a year. Do you think it was released bug free? Do you think the Gnome browser it uses protects your anonymity as well as TorBrowser? Anonymity is more than just pointing an app at a tunnel, especially when it is something as complex as a browser.