One thing to note about these is that they normally require custom drivers for even basic non-bypass use. Even in the unusual case where they use a standard Ethernet controller chip, a custom driver is still required to operate the relays (GigeE copper) or whatever method is used on faster port speeds to take it out of the default bypass mode. Those drivers are generally released only for a few versions of whatever operating system the boxes these were in used.
Also, they don't help at all if the system the bypass adapter is in needs to be moved for service and the cables don't reach, or the system is replaced entirely. After using these for a while in the GigE/10GbE space, I gave up on them and went to 2-port LACP trunks. One cable can be unplugged and plugged in somewhere else without taking that LAN segment down.
