[dnanian]

No, it's not a backup solution, but -- in combination with a full backup -- it is a solution to the "surprises buried in updates" problem.

By installing the system updates to a Sandbox rather than your main drive, you can maintain its pristine, "checkpointed" condition, while you check out the changes to the system. Once you're satisfied they meet your needs, you can apply those changes to the original volume.

Since your original volume is getting backed up (fully), your system retains its "known good" state... and rolling back from a "bad update" when using a Sandbox is a simple matter of restarting from the original volume: much easier than a "real" restore!