The new sleep tracking goes beyond basic movement tracking to include heart rate variability and other data. The result is far more accurate tracking that shouldn’t exaggerate the amount of deep sleep you get during the night. You don’t need to buy a new watch (it works with the original Vivoactive 3, Forerunner 645/935, Vivosport, Vivosmart 3 and Vivomove HR), but it’s good to know you’ll have it out of the box.
Garmin is shipping the Vivoactive 3 Music now for $300. That’s still not trivial if you just want music for your gym workouts, but it’s far more palpable if you insist on robust fitness tracking.