Thank you @Ray for the thorough answer! (and sorry for the delayed thanks)
That makes perfect sense… I tend to be a belt-and-suspenders guy, so the extra 4.7k resistor makes sense.
BTW I did actually switch to a plan where the flow sensor goes into a stock OSPi and the ESP32 acts as an extender only. This way I get a nice solid platform with the OSPi and also a faster platform to run any monitoring scripts, etc.
It’s a nice product.