Contact the seller for the exact pin out of the “USB2TTL connector (part of the bundle)”
Let’s say that the pin out is:
pin 1 3.3 Volt
pin 2 TXD
pin 3 RXD
pin 4 GND
pin 5 +5 Volt
It will probably be safe to use as long as you only connect 3 wires. That you never connect the first and last pin, because it could never provide enough current to power up the VF2.
pins
VF2 USB2TTL connector
6(ground) pin 4 GND
8(UART TX 3.3v ) pin 3 RXD
10(UART RX 3.3v ) pin 2 TXD (needs to be 3.3v TTL)
But an even safer option, if you only want to see the output, would be to use only 2 wires (there is never any voltage generated by the USB2TTL connector entering the VF2 board, so even if the TX pin on the USB2TTL was 5 volt TTL it can not cause any damage, if it is not connected):
VF2 USB2TTL connector
6(ground) pin 4 GND
8(UART TX 3.3v ) pin 3 RXD