The independence of a phone is a very strong selling point for the Amazfit. And while majority of my music is Spotify nowadays, 2GB space is plenty to last few workouts, just need to find those not DRM'ed mp3s again.
And indeed, the self assessment and features needed is most important. Unless you're prone to marketing and fashion. But then you're going to end up with the smoothest Pavlovian experience yet, AKA the Apple Watch. :D
I don't need music when I run or workout, but I don't mind a good podcast :)
Archive.org for the mp3 download it is for you then. Altho those "Pumping Iron" or BPM 150-170 playlists are enjoyable when... pumping iron.