Helpfull indeed 
With your procedure I also got the VTG over bluetooth only. (Using AOG Ntrip to get FIX at 10 HZ)
My problem was that VTG was only selected for USB.
Using one computer to connect U-center to C099 via USB (and power C099), it is possible to watch results in AOG simultaneously on another one connected via Bluetooth.
Example: If you change the number from 1to 10 (milliseconds?) for GGA, you see RTK fix speed slowly drops to 1 Hz!