The bit is only as harsh as the hands holding the reins. If the proper training and basics are taught it never need be harsh. Even the fattest rubber snaffle or even hackamores can be harsh in the wrong hands. If you look the curb is not being activated at all showing no harshness in this pic in any way. Look at the double bridle used in dressage. Those horses are not forced using those bits or they would never achieve the supreme level of relaxation it takes for the higher level movements. It can be harsh, but only if used harshly.