As far as I know, the standard tool for this is rdfind. This new tool claims to be "blazingly fast", so it should provide something to show it. Ideally a comparison with rdfind, but even a basic benchmark would make it less dubious. https://github.com/pauldreik/rdfind

But the main problem is not the suspicious performance, it's the lack of explanation. The tool is supposed to "find duplicate files (photos, videos, music, documents)". Does it mean it is restricted to some file types? Does it find identical photos with different metadata to be duplicates? Compare this with rdfind which clearly describes what it does, provides a summary of its algorithm, and even mentions alternatives.

Overall, it may be a fine toy/hobby project (3 commits only, 3 months ago), I didn't read the code (except for finding the command-line options). I don't get why it got so much attention.

See also fclones (focuses on performance, has benchmarks https://github.com/pkolaczk/fclones). I didn't know about rdfind but thought the standard was fdupes https://github.com/adrianlopezroche/fdupes, which is as fast (or slow) as rdfind according to fclones (and fclones is much faster).

fdupes is the classic (going way way back) but it's really very slow, not worth using anymore.

The four I know are worth trying these days (depending on data set, hardware, file arrangement and other factors, any one of these might be fastest for a specific use case) are:

https://github.com/jbruchon/jdupes

https://github.com/pauldreik/rdfind

https://github.com/jvirkki/dupd

https://github.com/sahib/rmlint

Had not encountered fclones before, will give it a try.