All USB-to-Ethernet adapters are pretty evil in my experience. Always terrible performance, often slower than WiFi.
USB-to-Ethernet adapters are life savers when you need to:
(A) replace your WiFi adapter - download drivers from internet
(B) configure a router or other equipment (hard to configure WiFi without WiFi).
(C) stand up your Linux install on your laptop (easiest way to futz around until you get WiFi adapter working - but check chipset on adapter is compatible which the cheapest usually are)
You don't usually care about the performance. Just keep a cheap one in your box of shit - I need mine often enough. If you need high performance, then buy a high performance adapter.
Not saying they're not useful for specific purposes. But anyone buying them hoping to improve performance compared to their WiFi, often comes away very disappointed.
In my case A) and B) are irrelevant because I only really own or deal with laptops now days, and they invariably have built in WiFi, but usually not built-in Ethernet!
I have a 2.5 GB/s USB to ethernet adapter. While I cannot say whether the performance matches that of built-in ethernet, transfer rates are fairly close to 2.5 GB/s. That is certainly faster than WiFi.
Oddly enough, point (A) is likely more relevant in the current world of laptops. At least if you use Windows. Plugging in a supported network adapter, may that be WiFi or Ethernet, may be the only way to get through the installation process, without jumping through hurdles, then install drivers for the built-in WiFi adapter, without jumping through another set of hurdles. (I own such a laptop, though I use Linux on said laptop so the WiFi just works.)
Your point makes no sense to me. A cable is often useful when WiFi isn't.
Case (A) is common for laptops. I've had plenty of WiFi modules (M.2?) go intermittent connection on friend's Windows laptops over time (maybe component drift?). For Linux on laptops I usually replace the manufacturers WiFi module so I get something better supported (high reliability - used to be Intel). Some people upgrade their module e.g. to get higher spec WiFi.
For (B), configuring WiFi routers is often easier with an Ethernet cable and sometimes necessary (depending on circumstances), and you need a cable to configure many other devices e.g. point-to-point links or whatever.
The fact you have a WiFi laptop is exactly why an adapter is really useful.
In my case, if I want ethernet it's because I want faster performance (reliably/continuously high bandwidth, and reduced latency and jitter) than my WiFi network can provide. But I've only been able to get that with a thunderbolt-connected ethernet adapter. Every USB one I've tried has been a disappointment.
I don't disagree that the uses you describe make them helpful in those circumstances, but I can't recall ever needing to do any of that myself. I'm happy with the built-in Wifi adapter and its drivers, and all modern routers can be configured/set up over WiFi, can't they? They create a default network when first turned on, or if you factory-reset them using the physical reset button.
Old custom software, old hardware, vendor wants all the $ for an upgrade, we refuse to pay. I took 10 desktop pc's($500 each) replaced servers ($20k each), one usb to ethernet dongle in every pc b/c we needed 2 network ports and we had this laying around, USB3 to GB, slap virtualization with USB passthrough. They work for 5+ years, gigabit speed, 24/7 with no problems.
People should have more faith in dongles. Not all are bad.
This is not my experience.
I have used many 1000BASE-T dongles and they work exactly as advertised - capable of transferring at ~950Mbps.
I have also used 2.5GBASE-T dongles and speeds are in the 2Gbps+ range.
WisdPi are even offering dongles with 5GBASE-T support (RTL8157 chipset):
https://www.wisdpi.com/products/wisdpi-usb-3-2-5g-ethernet-a...
It will depends on your USB ports.
I use 2.5 GbE USB adapters and they work great... as long as they're in the right port.
Half of the ports on my Thunderbolt dock are provided by a shaky ASMedia USB chipset and it drops or lags after an hour or so. The other half of the ports use a more solid Fresco Logic chipset and I left an iperf + ping running overnight and it was a solid 2.3 Gbit 0.x ms the whole time. The built-in Apple ports are also solid.
In my experience they always held up the 100 Mbit/sec claim for lower-end variants, and an acceptable 350-ish Mbit/sec on USB2-backed GbE devices. I have no experience with GbE USB3 dongles.
RTL8156B 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?
I remember in the Intel days, the Apple Thunderbolt 1 GbE adapter would have high CPU usage when you were transferring at the full 1 Gbps.
I've had good luck with the Realtek 2.5 GbE adapters, no CPU usage issues.
And these days even with a 10 GbE Thunderbolt adapter the CPU use is negligible, so things have improved across the board I think.
I've used tons of Realtek stuff since the early 2000s and have had only one single device misbehave - the infamous RTL8139 Fast Ethernet which had many bad batches unleashed onto the world. I have both bad and good versions of this chip. It burned a lot of people back then, many of whom to this day stubbornly refuse to grow up from their trauma, and keep saying that everything Realtek is bad and can never be trusted.