Another vote for photosweeper after I got multiple dupes polluting my Lightroom database. Happened when I changed mobiles over the years and all the cloud sync services cross copied older images eg. OneDrive, Dropbox, iCloud via Lr mobile. Some jpegs have multiple dupes! Photosweeper has powerful analytical criteria to search for dupes. Its selection panel lets you confirm which dupes to tag for deletion having cross checked any metadata or you can autodelete, but that's asking for trouble. I also received a note from the developer with updates for high sierra so it is actively developed.
It looks a bit simple minded but has powerful features underneath.