Had a Z2 for a few months now, sound is ok, but yes battery is "leaking" meaning if you dont shut down your Z2 at night, it will still eats up battery and you may end up with an empty one the next day, better turn it off at night.
The biggest problem, although it wont stop you listnening to music is ... the music app! still in v1, I dont believe Cowon has updated it, there are real issues, almost an unfinished product which is a shame considering its native quality, eg sound. So mostly:
- FLAC tags are not properly recognized
- 2 level tag navigation only, so genre > artist > album > song is not possible. the only workaround is to use folder navigation
To summarize, J3 was very good on these aspects. Z2 is bad, and you cant even use a 3rd party player, there is something wrong 3rd party players access music, with a good headset, you can hear gliteches, hiss and noise, which doesnt happen with stock app.
So it is either a poorly featured stock app with great sound or 3rd party app with poor sound.
Shame on Cowon, up until now they simply dont care ... I have to admit I am not sure my next player will be a Cowon ...