Booting from alternate drive before backup
 

I maintain a few SD! backups.... generally I just smart update the internal drive to a backup volume.
Is there any benefit to booting from a different drive, before then cloning my main drive to its respective backup - so no changes occur to the drive being cloned during the cloning??

The benefit is that you'll get a more accurate copy, since the source won't be changing.

Do you think this equates to real world advantages to the reliability of the clone??

Not in most user cases, no. But if you want to make sure that everything is in a fixed, known state, it's the way to go.