alt Hacker NewsRTL8156B does line-rate 2.5 Gbit/s no problem, most USB-C docks with network have a RTL8153B in them and that does line rate as well. Even mildly dodgy first-generation stuff like AX88179 generally works.
I.M.H.O. these USB dongles are actually preferable to the much more expensive Thunderbolt dongles praised below, because a) they work on regular USB ports as well b) they do not require Thunderbolt c) they use less power and d) they don't force a highly ventilated cooling mode on certain host systems. And, fwiw, at least some Thunderbolt docks actually used USB NICs connected to the internal USB controller, which was hooked up over PCIe.
I don’t remember the exact issues, but I remember seeing years ago my old Intel MacBook had noticeably higher cpu usage when connected to and using a Pluggable dock which had a Realtek Ethernet chipset. Switching to WiFi reduced cpu usage. AFAIK had something to do with bad and/or lack of hardware processing in the Realtek chipset so it had to do it on the cpu.
Now I never trust anything with Realtek in it, and if buying anything with an Ethernet port, I try to make sure it’s not Realtek. Is this still valid concern, or is Realtek better now?