I've installed this on my Mac by adding the folder with the .src files to the required directory and it works fine.
I tried adding the folder to %APPDATA%\Mp3tag\data\sources on my Windows device but the tag source was not showing up in the app. Adding the individual .src files to my %APPDATA%\Mp3tag\data\sources folder shows the custom tag under Tag Sources on Windows, but all searches return a "Sorry, no entries match your search criteria" error.