It will soon be added to Wear OS for Android smartwatches too. However, Spotify recently announced it'd be adding this very feature. The switch may be something you're minded to do if you were a reluctant Apple Music user who jumped across to iOS to take advantage of things like offline listening on your Apple Watch. You can also send your latest playlists back the other way – from Spotify to Apple Music – should you ever change your mind.
In an age of locked down ecosystems, it is admittedly surprising that there is still such a quick solution – so use it and value it while it’s around.