hehe, yeah, I believe that even with both Zigbee and Thread via MultiPAN RCP for simultaneous multiprotocol on the EFR32MG21 the highest baud rate used to communicate over the USB-to-Serial bridge in any current firmware is 460800, …so “fast” is maybe not the most important part as that still in the low end of what any USB 2.0 controller can manage 
If they should have highlighted anything specific regarding that CP2102N USB-to-Serial bridge it is stable, the official CP210x USB to UART Bridge VCP Drivers from Silabs, as well as the open source equivalent in the Linux kernel, are both mature and well maintained, and CP2102N support the ability to use USB discovery, …again, that will only work if they have written a unique USB product description to the EEPROM of the CP2102N → Community help wanted to whitelist all compatible Zigbee and Z-Wave dongles/adapters for automatic USB Discovery in Home Assistant