Greetings folks,
Today I was pleased to stumble upon this YouTube video:
https://www.youtube.com/watch?v=E39ECyCXJaA
Where the creator BeardedTinker outlined his own discovery of this helpful add-on tool. Where, in the past I would either have to flash these sticks using the Texas Instrument Utility on a computer, or SSH into my host and update over terminal. I found this method much easier and I did not have to go throughout my home unplugging and holding bootloader buttons. 
Here is a direct link to the github of the add-on:
https://github.com/mercenaruss/zigstar_addons
I followed the basic steps outlined in this video and was able to flash the firmware for my
- Sonoff Zigbee 3.0 USB Stick (CC265P) being used as a router
- Sonoff Zigbee 3.0 USB Stick (EFR32MG21) being used as a coordinator
Worth noting, while using the “ZigStar Silicon Labs FW Flasher”: (currently in version: 0.1.1)
I did enable “hardware flow control” and “Verbose Mode”.
As with most things, perform a backup of your configuration before trying this yourself.
Though, I did a quick search of the forum before posting here and hopefully more of us will find this add-on as convenient as useful as I did today!