Downloaded app while in vacation, mostly to have access to my son's favorite show, Teen Titans Go. So far, playing smooth, HD video, even on hotel WiFi.
Now, downloading it and installing it was a little bit tricky. A search for "Uverse" on the Fire TV stick returned zero results. Had to go to Amazon website, "buy" it and send it to stick. Waited for about 15 minutes and the app would not appear. Finally figured out I had to "sync" content in settings.
In summary, other than the not so straight forward installation, app working great. No buffering, no pixellation. IMO those are network issues, not app or stick related issues.
Some people complain about the content or lack of it, I'm sure that has to do with licensing from the actual channels.
Now I can watch uverse on all the TV's in my house. I have more TV's than receives, this app solves my problem.