The extract of the second case doesn't state he was cuffed, but he was, you'll have to accept my word on that or go look up the case.
Most department use of force policies do not specifically allow or prohibit the use of a baton on a cuffed suspect either. There are legal reasons for not getting too specific in a written use of force policy.
The actual question is "Should pain compliance methods be allowed on either actively or passively resisting persons who are already cuffed"? Why or why not. How may personal injury risks must officers take in order to physically control a restrained but resisting individual.
Ask your LE friends where the taser is on their department force continuum and whether it is above or below the baton. Would you rather be hit by a baton or a taser? Why? What are the injury rate comparisons between the baton and the taser?
Did you know that after the city of Miami issued tasers to all officers they had their first year of ZERO officer shootings after average 2-3 for the previous 14 years?
By the way, why would it be okay to tase a restrained but violent psychotic, but not a restrained but violent non-psychotic person? What difference should mental illness make in the use of force, if any? If a shock would get the attention of a psychotic would it not work even better on the non-psychotic to get them under control?
I can envisage certain scenarios where a taser might be used on an already restrained subject experiencing a servere, prolonged psychotic episode, if the effect of the taser helped to quell violent thrashing. The act would be in the subject's interest, in that case, since, by definition, he's out of his mind and requires treatment to become stable and end the episode. I'm not an expert, and quite possibly trained mental health professionals would dispute the efficacy of such an action. But to me it seems that in certain circumstances it might be reasonable, effective and ethical.
But violent, non-psychotic, already restrained subjects are another matter altogether. They're not out of their minds, they're just pissed. Their ability to sustain violent thrashing is orders of magnitude less than that of a mental patient, their ability to understand and communicate, orders of magnitude greater. They need to be restrained, but they don't need to be shocked. Eventually, they'll tire themselves out.
The police are not in the business of inflicting pain on anyone. They have the power of arrest, and important power, and they're sworn to exercise it professionally and judiciously. A restrained subject cannot harm a properly trained police officer, and a properly trained police officer should never consider it his duty or right to harm a restrained subject.