Random crashes and generally awful
I bought a new Fire TV and was excited to get a faster, smoother experience using Plex than I was getting from my three year old Roku. Imagine my disappointment then when, time after time, the Plex app on my Fire TV would crash and generally glitch out. If it wasn't crashing, it was unable to connect to my Plex server. It also lacks core features - namely the display of remaining video time - that I've grown accustomed to on my Roku.
Since Plex is THE core experience I bought this for, I returned the Fire TV and bought an Apple TV 4K instead. I haven't had a chance to use Plex on it yet, but I am sincerely hoping it's more stable than the Fire TV app. I know that Plex doesn't particularly care which device customers use to access their Plex experience, but they SHOULD care that their Fire TV app is so bug-ridden it's creating an extremely negative experience.