So, I went ahead and sprung for the Keyboard Book Cover for my new Tab S4. Other than the numeric keys being narrower than the letter keys and winding up offset to the point where, as a touch-typist, I have a hard time with them, it's decent.
I really wish the screen-off note feature of Samsung Notes was available when the tablet is in DeX mode. Switching from DeX to standard tablet mode requires manually turning off DeX -- it doesn't happen when you disconnect the tablet from the keyboard. So, unless I think to switch it off before I close the cover, it's sleeping in DeX mode and doesn't respond to the pen's tap-and-button-press to bring up a note page. Hopefully that's something that Samsung will fix in an update (soon, please!).
I watched the season 2 premier of Star Trek Discovery on the tablet this evening because I wanted to test out the sound system. Oh my. I think I'm in love. The audio quality was phenomenal! With Dolby Atmos turned on and set to "Auto", the audio experience was quite immersive.
So, at this time I've only got a couple of gripes with the experience, and they're not related to the tablet itself. First, the AT&T messaging experience has been complete crap. I switched back to their messaging app on my LG V30 so that I could do messaging from that number on the tablet but the backup & sync service hasn't done its job consistently, leaving me high & dry as far as sending/receiving messages on the tablet. Not Samsung's fault at all -- strictly an AT&T problem. My second gripe is with Google, who seems hell-bent on becoming mid-90's Microsoft. Their hunger for power and absolute control hasn't affected anything on the tablet yet, but it's sure hurt my experience on my phone. I'm sure it won't be long before their BS starts negatively affecting the tablet experience as well.