I'd be curious to also try out the feature that lets you build your own channel list from available free stuff and what you are subscribed to. I'm sure it has some positive features like being able to control what apps are installed and possibly how they are organized.

I imagine you'll find the firetv a bit slower for accessing things but possibly more convenient. Xfinity at times has free movie specials and other special events outside of the streaming apps. The remote works well and has it's own volume button and input button for controlling the tv which makes it pretty easy to use. There's no advertising on it like with my roku. I has the major free streaming options as well (Pluto, freevee, etc). I has pretty much every major streaming on-demand services but it more limited on the live services (I've not looked deep to see which ones are missing as I don't care about paid live services). The Flex box is locked to what services are on it and how they are arranged. Once the remote is paired to the TV is should take you to the TV input settings. Depending on the remote you have the TV input button would be located on the bottom right. The input settings would be from your TV options, not the box.

I use one of these Flex boxes on my main tv (it was free, figured I'd try it) and then a roku express on my bedroom tv. The connection itself from the box to the TV will provide HD quality.

Xfinity flex plex