Turn on and “Beep when a key is rejected or held down” . This single feature tells you why a letter didn’t appear (you didn’t hold it long enough vs. you double-tapped too fast).

This is the #1 reason people enable Filter Keys. It prevents a single accidental brush of the keyboard from typing a letter.

This stops a single key press (like S ) from typing ssssss due to a shaky finger.

Set to 59 (This "On" flag value is widely used to ensure all necessary sub-functions are active).