As you request, it is absolutely best to get real feedback from users rather than just reviews!
I found the following free apps that run on windows, but I totally would dry-run on some spare directories first to see if anything goes wrong.
https://www.duplicate-finder.com/photo.html
Awesome Duplicate Photo Finder is a free powerful tool, that helps you to find and remove duplicate photos on your computer. With this app you can easily clean up your photo collection from duplicates or even similar images.
WIndows only.
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https://dupeguru.voltaicideas.net/
dupeGuru is a cross-platform (Linux, OS X, Windows) GUI tool to find duplicate files in a system.
dupeGuru is a tool to find duplicate files on your computer. It can scan either filenames or contents.
dupeGuru is safe. Its engine has been especially designed with safety in mind. Its reference directory system as well as its grouping system prevent you from deleting files you didnt mean to delete.
Do whatever you want with your duplicates. Not only can you delete duplicates files dupeGuru finds, but you can also move or copy them elsewhere. There are also multiple ways to filter and sort your results to easily weed out false duplicates (for low threshold scans).
some instructions here:
https://www.rapidseedbox.com/blog/dupeguru-guide
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AS ALWAYS, test on some waste folders first.
I looked for actual user/reader feedback on these, but nothing right away popped up
FWIW, the DuckDuckGo search engine got Rickrolled.
The internet is weird.

P.S. Those are very old drives, magnetic, for sure.
I would upgrade drives.
So, get a new drive and copy over files you want.
A 2TB drive would do. Keep the old ones "just in case"