The first Agonizer was developed and marketed as a behavior modification tool. It functioned much like a shock collar on a dog. If the device detected a proscribed activity, it would deliver a painful shock to the wearer. It was engineered to help people avoid bad habits such as drinking, smoking, or eating to excess. It proved unpopular with its intended audience. Military, psy-ops, and intelligence agencies.
Pain is Cheap
The true Agonizer is a device, typically attached to the chest, and linked to the gesund auf of the user. The device can then measure the biofeedback of the pain it is inflicting and adjust. This prevents the device from killing the user, but also prevents the user from developing a tolerance to the pain the device inflicts. With tech synchronization, the Agonizer can be linked to the CogNet, allowing outside agencies to access the device and control it.
Cheap has be regarded as a primitive and not particularly effective as a means of controlling people. That might be true, but pain is cheap, and the means of inflicting it are many. The agonizer, that's a cheater's tool. It takes the torturers art and gives it to a machine.
The Penal system has found the agonizer a great tool for controlling unruly inmates. This is not done in the first world nations like the Atlantic Federation or the Pacific Rim Coalition, but in second and third world nations, this is much more common. Agonizers aren't grafted onto common and petty criminals, they are reserved for political dissidents, terrorists, and members of oppressed minorities and factions. The one upside to having an agonizer is that the device is tied to a health monitor, so inmates with these devices are seldom abused by guards or other prisoners, for fear of being caught in the act.
Interrogators, both police and intelligence agents, have used agonizers to interrogate prisoners. This is seldom done in a brute fashion, but rather as an accessory in breaking a person so that they will divest whatever knowledge they have. Confessions are considered useless, but most questioners are looking to either convert the victim to their side, or to gain concrete intel. This is questionable at best, as many will say anything to make the pain stop, even if it means creating elaborate lies or complete falsehoods. This is almost completely unheard of in first world nations. It is much easier to use a brain hacking AISC to gather intel from a victim than to rely on centuries old pain application techniques. Criminals and organized crime syndicates are more likely to use these devices for this purpose, along with dictatorial and totalitarian regimes in the 3rd world.
Conscription and criminal based military units will use a variant of the agonizer to keep their soldiers in place. Half of training involves military tactics and weapons, the other half is being abused and terrorized into staying at their posts and in their units. Such units have very low morale, high suicide rates, and other cohesion problems, but then such units are typically used as meat shields for regular army units.
In countries where clones are considered sub-human, it isn't uncommon to find them fitted with these devices. Should a clone threaten a resident, or simply inconvenience them, they can inflict pain on the clone for their transgression. Such things are considered barbaric, and are generally limited to offworld colonies and habitats associated with secondary or tertiary global powers.
By simple inversion, an agonizer can be configured to induce an orgasmic state. While this might seem highly desireable, in practice it becomes a much more sinister and negative thing. By removing human contact, emotional connections, and even basic dignity, the victim of the pleasurizer loses their desire for or appreciation of intimacy. Those who have been fitted with the rare pleasurizer often are interrupted doing involved tasks, or are forced to into dangerous situations while callous spectators watch, with their fingers on the trigger. The push button orgasm seemed like a fun idea until it was used while the victim was trying to walk across a balance beam above a pool of sharks. He shuddered, lost his balance, and fell. The next victim in line wept as she was forced to cross the beam, knowing what was coming.
The Agonizer has a limiter to prevent the device from killing the victim. The Euthanizer is designed to specifically kill the victim. It is a one shot device, when the signal is sent it forces the victim into a full body seizure and cardiac arrest. If there are medical personnel present, the victim can generally be revived, but only after the Euthanizer is fully discharged. This has seen greater deployment than cranial bombs, as it requires much less surgery, is much less expensive, and many victims of headpoppers have gone against their orders simply because it is a quick and painless death. The Euthanizer is a much slower, much more painful death.