Masters of only one (Let Kindle Slide). Online Shopping. I simply do not understand all of these devices that Amazon is trying to pimp. Phones? Tablets? I love shopping at Amazon but their brain dead hardware makes zero sense.
I actually like the Fire TV--it supports everything I need (I like Apple, but I'm not invested in iTunes movie purchases and rentals, and Amazon Prime is quite nice for both movies and TV), and it can side-load Android apps, which isn't always useful but is at least a little fun. The Fire TV Stick, recently released and much cheaper, might also be nice, but I haven't used it. I actually returned my Roku for this. As you possibly hint, the Kindle is also a nice device, though I mean the e-ink variety rather than the tablets (which may also be nice, but I have never used them but suspect I would much prefer my own tablet with the Kindle app, which I currently use if I want an LCD).
As for the Echo, if it can be used as a high-quality speaker, I can see it being useful for that, though it would be nice to have a physical connection rather than Bluetooth. Its intended main function sounds neat, but I'm not sure it will be that useful (and I'm not sure how I feel about having an always-on mic, even if it presumably doesn't transmit anything to Amazon unless it thinks you've beckoned it).