Rockbox has made its appearance in 2002 on the Archos firmware with manufacturer contained many gaps. Since then he has continued to evolve to become compatible with many readers and few now accept many plugin to add numerous features to devices that support it. It just make such device compatible with the Game Boy, PDA functions gives them, providing them a variety of applications and utilities ... it has even given access to the movie has some device that was free!
Another advantage is that it is not necessary to remove the manufacturer for using Rockbox firmware. Using a combination of keystrokes, you will have the opportunity to leave your reader in a traditional manner or using Rockbox.
In short, use Rockbox has only advantages. In addition, the Sansa Fuze, it does not replace the original firmware but moved in parallel.