As the author of the tool, thanks a lot for wonderful inputs! Many comments are actionable. I'll incorporate them in code soon.
Now to address a few concerns:
# The tool doesn't delete anything -- As the name suggests, it just finds duplicates. Check it out.
# File uniqueness is determined by file extension + file size + CRC32 of first 4KiB, middle 2KiB and last 2KiB
# Above seems not much. But, on my portable hard drive with >172K files (mix of video, audio, pics and source code), I got the same number of collisions as that of "SHA-256 of entire file" (By the way, I'm planning to add an option in the tool to do this)