I've used SuperDuper for few years now with no issues. You should be able to use SuperDuper with your Time Machine backups, though this creates a disk image so you won't be able to look through the files in the backup. Also, iirc, if you go the disk image route, SuperDuper will have to backup the whole thing each time, as opposed to updating only things that changed (which it can do if provided with its own partition/drive).