Amazon has just put the official Ethernet Adapter for Fire TVs on sale for $10.99. If my memory is correct, this is the first time that it has ever been on sale. Amazon has offered it at a discount in the past when buying it along with a Fire TV device, but I don’t believe it has ever been on sale on its own. The Amazon Ethernet Adapter is compatible with the current 2nd-gen Fire TV Stick, the Fire TV Stick 4K, the 3rd-gen Fire TV (Pendant), and the Fire TV Cube. It plugs into the micro USB port on those devices to provide a wired internet connection so that you don’t have to rely on WiFi.
The Amazon Ethernet Adapter is a 10/100 speed device, but because it connects through a slower USB 2.0 port, you’re only going to see speeds around 80 Mbps. A solid 802.11ac WiFi connection will get you speeds above 300 Mbps, so the Ethernet adapter isn’t your best option if speed is your concern. Since all streaming services require well below half of that 80 Mbps cap, you’re not going to see a negative difference by lowering your theoretical maximum speed by switching from WiFi to Ethernet, unless you’re doing a lot of web browsing or local file streaming on your Fire TV device.
Where the Ethernet adapter really matters is in connection stability. Even a good WiFi connection has occasional hiccups. An Ethernet connection is more reliable and consistent.