How can I smooth down the display, e.g. BoxFlow or Thermometers so they are not so fast?

BoxFlow, and all the "jumpy" displays can be calmed down by using a new control, which is the "Global Smoothing Window" in the Frequency Bands control panel.  Set it to a higher number, such as 500 milliseconds or even 1000 milliseconds, and the system will be much smoother.  It defaults to 60 milliseconds, which is quite fast, and gives feedback for each little burst of the wave. You will likely prefer a longer number, which also smooths out the sound feedback to be more steady, less erratic.