The real focus here is a "Heads up" about the update and a reliable way to recover via the battery/reload firmware. Great post.
But for the sake of future reference, this also might be a good place to mention:
On the original ST16 you can scroll up/down on the android recovery screen using the volume control buttons. Swipe to the left (not press or tap) for both the "+" (scroll up) and "-"(scroll down). Note you swipe left for both "+" and "-".
"Enter" is a quick off/on cycle of the power switch. (As you noted above, the power switch does not work as an "off/on button" when the android recovery screen is active. It will not turn the controller off if you do it too slowly. But it may not trigger the "enter" command.)
I am not certain this will work the same on ST16S. I don't have a way to try it.