In an attempt to get this working (and get the 9600baud firmware installed), I have followed the instructions to flash the firmware (but then on a Mac), but unfortunately without success.
I downloaded the firmware from the github page, opened up the device, and powered it up while pressing the boot button. I had to install a different version of stm32flash (using homebrew) as the one in the pingviewer.app folder gave me an ‘exec format error’. I found the device name using ls /dev/tty.* and double-checked the name with the logs. Then with the LED off, I then ran stm32flash, but got a Failed to init device.. Also tried it with a 115200 baudrate (-b 115200) and 115kb firmware file, but the same error.
$ stm32flash -v -g 0x0 -b 9600 -w ./Ping-V3.27_9600b.hex /dev/tty.usbserial-DM01NJ2Q
stm32flash 0.5
http://stm32flash.sourceforge.net/
Using Parser : Intel HEX
Interface serial_posix: 9600 8E1
Failed to init device.