FYI, apparently the engineer of this ITead stick missed connecting RTS and CTS between the EFR32 chip and the CH340E chip, meaning it will not be possible to build firmware with hardware flow control:
https://github.com/xsp1989/zigbeeFirmware/issues/15
You will of course still be able to use software flow control with ZHA and that should be to work as well from an end-user perspective as long as all other components are properly implemented and stable.