[Kodroid]

I've been using the UGREEN USB 3.0 Hub Ethernet Adapter 10/100/1000 Gigabit Adapter on my Fire TV Stick 4K since day 1, never a single issue with network or device instability.  Using this adapter via the USB 2.0 port on the 4K requires a microUSB OTG cable such as this one.  The UGREEN Network Adapter USB 3.0 to Ethernet RJ45 Lan Gigabit Adapter would also work just fine if you don't want the additional USB ports.

Using a USB 3.0 Gigabit Adapter on the 4K gives me a stable 320-330Mbit download when I test via analiti on my gigabit network connection and buffer free streaming of files with greater than 50,000kbps data rate over my network via NFS from my Linux file server. 

If the Wi-Fi does not work well (I ordered my Ubiquiti AP yesterday: P), I will switch to wired gig.
Thanks ! 

The Fire TV 4K stick has the best Wifi I've seen in any streaming device I've owned. I do wish they would make another FireTV box in the future, though so we don't have to buy wired adapters.