How to backup applications' data from second or subsequent user of a currently non-rooted device?
I use Helium on a non-rooted Nexus 7 (2013) to backup my app data (but not the apps). I have only one user account but since that app data is user-specific, is contained in my user area, and the backup is placed in my user area, I'd be surprised if Helium would have any trouble backing-up each account separately. I have not had occasion to restore a user's data from a Helium backup, so be I can't vouch for that process.