Is it okay to run two instances of SuperDuper! at once?

It's quite easy to start two instances of any app from the command line. In this case: open -n /Applications/SuperDuper\!.app However, I know that this isn't always a good idea because most applications are not meant to share resources with themselves. I was hoping to back up two different drives with SuperDuper! (a hard drive cloning application) at the same time. I was wondering if this is safe.