I can confirm that this method works almost perfectly (thank you). There are, however, two issues with the MM script. The first is that it doesn't export Last Played dates, it needs to be modified to write Play Date UTC into the output to get this data into MB. The other which I think is also a script issue is that the script does not handle special characters well, so any song, artist, album with letters with accents (eg Emile Sande), or with apostrophes, on import will show as not found (as MB cannot match the data imported to the file). I found it easier to use MB to find the file than to modify the script so can't help with a solution.
The MM script is also intended to run every hour by default and the output takes a bit of hunting down. I found changing the settings so it ran on shutting down MM was the easiest way to know it had extracted the data as there is no dialog only a progress bar. Once it is extracted it imports into MB sweetly with Date Added, Last Played (if script modified) and Play Count intact.