Jointed shanked bits can also be quite confusing to the horse, especially if the rider is not educated on how the bit funtions.
You can't really direct rein with shanked jointed bits, because there's no way to control when the leverage action of the bit is applied. You can't really move the bit back and forth in the horse's mouth, the way you can with a snaffle.
The only time I don't mind jointed shanked bits, is when they are a used with two reins (curb rein and snaffle rein), in educated hands. That way the rider is able to control whether the curb action or the snaffle action is applied ;)