Misses most embedded images and many attachments. This forced me to do a manual scan thru each mbox and save them explicitly.
The program cannot even copy straightforward text-format messages from the MBOX to individual files (exporting as plain text) reliably. Numerous newline characters were stripped. It is easier for me to work with the MBOX files in a text editor when I want to do things in bulk.
In sum, it is faster to work without this add-on than with it.