For those wondering how these work, well I've found they work pretty well.
- Music : you can choose the music app you want to use via GCM and then the watch can play/pause, choose next/previous as well as control the volume. This is accessible while you're running but might be a bit fiddly to get to. If you're using a Bluetooth headphone it will be easier to use its buttons to control the music.
- Audio feedback : when you hit the lap bottom (possibly Autolap, haven't tried) you get the lap number and the actual time in minutes and seconds. If you're listening to music it will be faded automatically. Works well and reminds me what the Nike app did.
Hopefully they will come to the other recent Garmin watches like the FR920 and Fenix3...