I built FileLever as a preview-first tool to review all the changes before a sync or backup runs. FileLever works with local drives, external HDD, NAS, USB drives, SD cards, Dropbox, locally synced Google Drive.
Filelever started as a folder comparison/sync tool, but I have recently added Apple Photos archival workflow to the growing list.
Take a look and let me know if you would like to see something more in this tool, especially from anyone here who manages large photo libraries, external drives, or backup folders.