I do (came with the tablet, I didn’t select it). I use it to charge, otherwise not much. If you have a good place for it, the speakers in it are nice (for their size anyways). It’s a bit of a gimmick I think
I have as Pixel Tablet currently. I use it to read, and watch Jellyfin. I don’t find the speakers or screen bad at all. GrapheneOS should work (I have not tried that yet). Support goes for about 4 more years (less than the 5 you are going for, but close). It’s not a bad choice I don’t think.
If the dock had an adjustable angle, I’d use it more. Its fixed angle kills some utility. I’d skip if possible