I have yet to see a GUI variant of deduplication software for Linux. There are plenty of command line tools, which probably can be ported to macOS, but there's no user friendly tool to just click through as far as I know.

There's value in convenience. I wouldn't pay for a yearly license (that price seems more than fair for a "version lifetime" price to me?) but seeing as this tool will probably need constant maintenance as Apple tweaks and changes APFS over time, combined with the mandatory Apple taxes for publishing software like this, it's not too awful.