I have a pre-facelift Model S with AP1 so the first generation MCU1.
This update brings a lot of things that arrived in time for Christmas elsewhere, for example enhanced voice recognition and backgammon (I went from 2019.40.2.3 to 2020.4.1).
A quick test of the voice recognition revealed it was a bit glitchy - sometimes it was completely deaf to my voice, sometimes it misheard and sometimes it was okay, for example I occasionally got the wing mirrors to fold and unfold and switch heated seats on. It would only increase temperature, never turn it down or switch things off though. So a step in the right direction but very beta. I am pleased that they have made it available for older cars though and still hold out hope that one day I'll be able to turn on front/rear fog lights without glancing down to navigate the touchscreen.
But the most unexpected bonus appears to be the web browser which is widely reported to be working on MCU1 cars now, and I believe the main map is now a lot more responsive. If both remain stable I see it as a big bonus as I thought the developers had given up doing any optimisation for MCU1, which seemed to be struggling to cope with the V10 operating system.