The application works great. The man page and online help could use a little clarity, but then this is Linux and not BSD.
Key items: only sectors with actual metadata or file data are backed up. A 60GB filesystem that is 10% full will be a 6GB backup, that may be compressed with gzip or anything else handy.
Note:
To restore requires the same size partition (or greater) than the filesystem backed up. So that 6GB backup example requires a 60GB+ partition on restore.