Just got my Bluetooth cable in the mail today. My ZS3 is the old version so no joy there but I kinda expected that anyway. On the ZS5 my initial impression is not bad sounding at all. More than adequate for a workout setup. Unfortunately, I'd hoped pair it with a Benjie K8. The BT implementation on the K8 seems super-kludged together but it does work. Pairing went OK but when the device moved to arms length away from the KZ module everything just crashed. No connection lost indicator from either device but no sound.
This was disappointing so I connected the KZ Bluetooth to my Kindle 7" HDX tablet. Here, there was no disconnect even walking from room to room about the house. Then I connected the Benjie to a pair of audsom M05 APTX. Again, no lost connection walking about the house.
As for sound, my first day impression is that I prefer the KZ module to the audsom though that comparison--over ears vs. IEM doesn't mean much.
Will report more as I play with the KZ's battery life.
Good to know the Bluetooth cable does work ok, I think I'm gonna buy one along with the ES3, according to some it has better bass, vocals and mids than the ZST. Hopefully the battery lasts at least 4 hours.