I wouldn't be surprised if thier software actually stopped you from using windows backup, unless you purchased the "premium" version.   I say this, becuase from fresh install, my m18x-r2 we have , does not work with widows backup. always giving us an error near the end, and nothing we do seems to fix it.
Just how long (know it is hard to estimate accurately) should it take to back up computer using the Dell DataSafe Local Backup.  Used it yesterday, and took about 10 hours!!  New computer witihout much on it.  Thanks...
Dell DataSafe local backup