These are the names of the Calibre fields.
Seems like to get it to refresh on the Kindle you need to delete from device and re-send. (I think I’ve misunderstood this, though.)
Currently trying out Yomu, which doesn’t seem to have any horrible things about it yet
If you don’t sign in to Amazon, you can’t download dictionaries, and it gives you an annoying popup each time you navigate to your library.