I’ve also had some compatibility and driver problems with the Ethernet-to-USB adapter. I had the best experience with the Delock adapters.
However, I only use such adapters when I need a second Ethernet Anschluss on a laptop, because for me a laptop without an integrated Ethernet Anschluss is a no-go. Because what use is it to me if the device is a few millimeters thinner and a few grams lighter and I have to carry adapter boxes and cables with me?
The easiest method for speed testing on the LAN is to use very large ISO files. If you transfer such a file from one PC to another, the operating system’s “Spedometer” provides sufficient accuracy. You can also use the freeware JPerf, but it hasn’t been maintained for years and it works depending on the environment.