macOS Big Sur appears to be using a Driver Extensions (DEXTs) to provide support to most USB network adapters built with Realtek chipsets. This allows for simple plug-and-play compatibility. But my testing has shown than CPU usage is excessive with the Apple provided DEXT. It interferes with normal system operation. For example, it causes stutters in system audio. Furthermore, on gigabit or faster connections, the DEXT is unable to reach actual gigabit speeds, instead reaching actual performance that typically tops out between 600 and 700 Mbps.
I noticed this behaviour first when I purchased an OWC Thunderbolt Dock. But the performance issue is present in most USB network adapters with Realtek chipsets that I’m aware of.
The performance was unacceptable so I searched for a workaround and found this Plugable adapter. The Plugable adapter’s performance is top-notch, reaching full gigabit speeds on my Internet connection. Furthermore, CPU usage is a fraction of the other network adapters that I’ve tried.
When I dug into why this may be the case, I noticed that the Plugable adapter – while still totally plug & play – does NOT use the problematic DEXT. Instead, it seems to use a regular kernel extension.
As kernel extensions are on the way out, I’m wondering if Plugable is aware of the performance issues with the standard driver extension? I’m worried that future versions of macOS will deprecate the KEXT that the Plugable adapter relies on, resulting in the same problematic behaviour.
That said, for the time being, those Big Sur users observing sub-standard performance from your other Realtek-based network adapters can rest assured that the USBC-E2500 is a trusty workaround. It will work reliably and perform as expected.