If you are using or thinking about using speffz for blind solving the 3x3 cube (or any size really), you can use this App to improve your recognition time for sticker pairs.
Choose from either free practice or three timed modes (1min, 3min, and 5min) that will record your high scores. Youll be presented with a sticker pair and you answer by choosing the correct letter on the speffz keypad.