If one picks the wrong option while in Registry Backup, one gets a blank notepad window. If one picks the wrong option while in Files Backup, nothing happens. This is minimally confusing also.
Your solution provides a neutral, factual feedback from the program. It will also work with Other Backups (which can contain both registry and file items in the same backup structure), with these exceptions:
If the C&FMC backup was only for removal of empty folders, there is currently no option to list those. Of course one could use Explore to navigate to dirs.dat.
History cleaner backup can have both registry and file items, or just one kind. If it just has file items, the entries.reg has only a TBackupManager header.