That keeps track of play counts on both devices, lets me make smart playlists and playlist folders, and syncs music, contacts, and calendars all over USB without any cloud services prying into my personal data.
Apple went from being a leader in the music-listening industry with excellent UX to trying to compete with Spotify and YouTube, who are frankly not even that great (e.g. trying to keep playing a song in the background).
Flash memory was small when the iPhone came out in 2007, so everything moved to streaming. Now the capacities are finally big enough again (e.g. 128GB iPhone SE), Apple's broken their sync services.
I like having play counts, ratings, and playlists, and I like that I've continually built up my music library since the days of Soundjam MP for the Rio 600.
Doppler is trying to put a new theme on Finder's MP3 playing feature, but it's not the syncing library manager that I need.