The move to a JK Hiface MK2 was precipitated by my nagging awareness that the MK1 still had some improvements outstanding that could be applied to it:
it still used the 5V power from USB for some circuits. When I applied external 5V instead of USB 5V it did improve the sound. I advised some MK1 users how to do this by cutting into the USB cable & tapping an external 5V supply into it - effectively dispensing with the noisy USB supply from the PC.
Charging the LiFePO4 battery is a bit of a pain. LiFePO4 chargers are not yet widely available.
The MK2 fixed both of these niggles and comes with a 5V supply and a LiFePO4 battery charger already inside the box. There were one or two other improvements too. All this improved the sonics once again - in making the MK2 immune from the low quality of the PC's power supply and the kind of USB cable used. It also made it a more user-friendly, device.