I just wanted to send along my kudos for the new font metrics APIs.
I had to create my own font metrics tool to perform this functionality for a current app, which we intend to put into more than 50 languages. That said, I found that so many English fonts has issues, too - not to mention the international fonts to support large characters.
Do you have an internal list of fonts that were used in the testing and creation of the new plugin? This could be very helpful, as I found that sometimes fonts didn’t appear to have the proper default values and I needed to create them with my tool.