It currently poses as an example on how to code plugins, but you can already install it and it should work fine. In the future I might integrate it directly.
Very weird, which version of BTT & macOS are you currently running? ( I know that the plugin was installed by other users in the forum successfully already, but maybe some specific bug)
It looks like there is a bug with the double-click installation process on 12.5. Could you try to copy it to the /Library/Application Support/BetterTouchTool/Plugins folder manually and then restart BTT?