Comparing them both right now. Same slick interface as the FireTV. For those who have a FireTV, you will notice it does move slightly slower and buffers up media ever so slightly slower as well (this one shows a buffer "circle" for a second or two where the FireTV does not). Not really something to complain about, because it is still very fast. The remote feels lighter and cheaper built than the one that comes with the FireTV, but feels like a quality unit and you can use a phone app to control it as well (including voice control) if you like so that's sort of a moot point. It supports screen mirroring and "second screen" while mirroring, which allows you to control the unit and see additional information about what you're watching while it is playing as well as browse other apps on the tablet/phone while the main screen displays the media. Like their tablets, it is already pre-configured for your Prime account so getting started is quick.
Initial impression? It is a pretty impressive unit for the price. It feels like you're getting a lot for your money even at full price. Nits to pick? USB power cable could be a little longer, but since the wall wart is USB, you can probably use your own cable. The unit is fairly long so it wouldn't fit into the space where my HDMI ports are on the back of my particular TV - they include a short extension cable to take care of that and that worked for me. Audio to the AVR will have to be via ARC or an optical feed from the TV, since the unit plugs into the TV (would it work connected directly to an AVR then is the question).
Got my shipping notice for the other one for Friday delivery