version 2.1 is out, it is is only a small bugfix. The custom tags are duplicated from song to song during scanning (thanks to Mike for reminding me).
Currently I don't use the MM4 version, so if something isn't working don't use it.
Some words to autotag samplers - most times you get a bunch of false results. This is a problem of AMG not from this script. I send the album title to AMG and if the album is not in the result list I can't do anything. Try it yourself.
But you can search manually in the main window until you have found the desired album and then press rescan. Most times I do it for every album I have, due to the mass of different releases for a single album, UK-Release, German release, 1 bonus track, 2 bonus tracks, remaster, reissue, etc. etc.