If you already have a Fire TV and an Echo device, then the Fire TV Cube will not really be that appealing to you. I have a first generation Fire TV, and Echo devices in every room in the house, except the bathroom. There is nothing I cannot do with the new Fire TV Cube that cannot be done with an Echo device and another Fire TV device, except turn on my TV and AV receiver, which is nice.
I bought the Fire TV Cube to finally upgrade to 4K. which my first generation Fire TV does not support. The Cube does have 16 GB of storage, which is better than the 8 GB that is currently found in the other Fire TV devices, but it is not stellar. The internal CPU and GPU are alright, but nothing that other Android TV boxes don’t have. The device still only has 2 GB of RAM. They really need to upgrade the RAM to 4 GB, which would make it run a bit better.
Bottom line, if you already have a 4k Fire TV and an Echo device, then there is no point in getting the Cube.