Bdbb
That add-in is for backing up the backups. It takes a copy of the system backup files and registry entries.
If the main system drive fails, you need to do a reinstallation of the os and currently I am not aware of anything that backs up the os partition of that drive. In other words, reinstalling the os means that you can lose add-ins installed and if you have installed any apps via rdc, you need to reinstall them, you need to reset users, etc. WHS has a pretty good methodology for restoring.
As far as data is concerned, if you enable duplication, data is saved to different physical drives. If a data drive fails, the data is rebuilt from the other drive when a new one is reinserted. You can also back up the data on the shares to either an unmanaged drive or an external drive.
Hope that helps...
Jim