But I would never suggest that you use in-spin aileron. YMMV
In-spin aileron typically does help recover a flat spin more quickly, and that is commonly accepted. However, it should be noted that there is an important distinction to be made between
emergency spin recovery technique, and
active spin recovery technique. Active spin recovery assumes the pilot has the wherewithal to apply each control exactly as needed to effect the most
efficient recovery. In-spin aileron does help with that in most airplanes.
However, if a flat spin is accidental, and you have lost control of the airplane, it's best to revert to an
emergency spin recovery technique, which is designed to minimize the amount of situational awareness needed. These issues are typically related to spin training in the aerobatic commmunity, and this is widely accepted --- there are only two recognized
emergency spin recovery techniques. 1) The hands off 'Beggs-Muller' method which involves pulling power off, applying opposite rudder and completely letting go of the stick, and 2) The neutral control method that involves pulling power off and visually neutralizing all controls. Whichever method you choose to revert to should be known to work for all spin modes in the aircraft type you are flying. All are a little different.
Emergency spin recovery is a very different concept from that of the aerobatic pilot doing deliberate, perfectly controlled spins, to known outcomes. I too, would not recommend in-spin aileron be used as part of an emergency recovery technique...just as I would also not recommend power be left on. But the skilled pilot can learn active techniques to extract more performance and precision from the airplane. Just be willing to pull an emergency technique out of the bag if necessary.