Hi
Unfortunately I haven' used StarTech USB 3.0 to Dual Port Gigabit Ethernet Adapter but their website https://www.startech.com/uk/Networking-IO/usb-network-adapters/USB-3-to-Dual-Port-Gigabit-Ethernet-Adapter-NIC-with-USB-Port~USB32000SPT
suggests
"The dual USB NIC is also ideal for providing dedicated physical network interfaces to virtual machine configurations. Great for IT administrators that require dual-homed or multi-homed host systems."
Based on above, If you are thinking to have two virtual machines running on your host operating system, on vm using one virtual switch configured to one RJ45 Gig Ethernet port and second vm to second, that should be fine.
If your pc has multiple Ethernet card and you open a command prompt and ping or tracert. The packet forwarding will be based on the routing table entries your pc have in the output of netstat -nr.
Regards
Zaaf