@Jordan We haven’t gotten an Ethernet bridge to work on the Raspberry Pi, we have been using some small Tenda 5-port Ethernet Switches for some Ethernet payloads we were testing a few months ago. At the time we were only test the white standard 5-port Ethernet switch (S105), but I see now they added on a Gigabit switch as well (SG105). The standard switch was like $8 on Amazon.
We removed the white plastic case and just installed the PCB on top of the Fathom-X. The power input is 5V so we hacked off a short section of the included power adapter for the barrel plug and connected a UBEC to it.