It works incredibly well! Just play the music through Xbox Music or anything really, tap on the icon for this app and it will instantly show you the lyrics to the song playing! It also gives you the option to browse your whole library and view the lyrics to all your songs in your collection! Check this out, its quite nice! You can even play your songs from the app itself
Even though they are both excellent apps. But both do not search existing lyrics in the tags of the music files.
music+ seems to link tags to the songs, not actually embed them itself.