While I can appreciate that much of Mylio’s speed comes from writing metadata like “title,” “caption,” and “keywords” to synced XMP files, I would still like to see an option to always write that metadata directly to a file. I would suggest it be disabled by default, to preserve the speed benefits.
I do use the keyboard shortcut to save the metadata to the file (when desired, and when I remember), but that option doesn’t exist on iOS. However, if there was such an option, the desktop version could recognize the changes made on iOS and update the file accordingly.