Rdiff-backup is based on the rsync-algorithm, but it doesn’t use rsync. It’s way of storing differentials is completely different from that of rsync-using scripts: it only stores the block-level differences between file revisions, where rsync scripts store a new file everytime you change a file.

As for rdiff-backup GUIs then, perhaps I should look at rdiff-backup-web or rdiffweb at some point.