I have a different experience, but I have also stopped using USB —> Ethernet adapters.
For years, we have used cheap 11” laptops with USB adapters in them for about 20 branch office routers. They are inexpensive, include a screen and keyboard, plus a battery backup and a wireless card. They have worked quite well for us, and while we did encounter a few USB to Ethernet adapters that gave us trouble, it was quite uncommon. My favorite one is the Apple USB adapter, which seems better made than the others, and has never given us trouble.
Having said that, in recent years, these low end laptops have started limiting the number of USB ports available, and none of them include a built-in LAN card as they used to. This means that there are only two ports available, limiting you to Red and Green, with blue on the built-in wireless, but many of the wireless cards don’t work with IPFire and HostAPD, meaning that you need an external WiFi Access point.
Similarly, The IPFire Mini Appliance has since been introduced, and I recently bought two, along with wall mounts, wireless cards and a serial cable. The cost was just over $400 for proper dedicated hardware with four built-in Ethernet ports using a chipset chosen by LWL because it will work at maximum performance and reliability with IPFire. It’s far superior from a hardware point of view, and I wouldn’t go back. The HP machines you mention in your post are great machines, and if you are careful with your network hardware selection, you could get the same performance, and save a little money. However, I will gladly pay a little more to have the compact form factor and hardware selection benefits of the Mini.