I realize this is an old post, but this should be corrected. unixSecLab is, unfortunately, mistaken. I have one of these and can confirm that one may only obtain a single direction of network traffic with an individual output port. In the Hak 5 description of the device, this fact is actually mentioned:
"2. Use Ethernet cables to connect one or both of the monitoring ports (J3 and J4) to ports on one or two monitoring stations. Each port monitors traffic in one direction only."
URL of Hak5 Throwing Star Lan Tap: https://hakshop.com/products/throwing-star-lan-tap
