Yeah liquid diet is not a cure for being fat or for bad eating, because there is plenty you can drink that will make you fat still. Like Milkshakes.
The patients in the trial were all issued with an emergency key to allow them to disengage the device themselves if they had a problem with it. They could have just used the key and gone out and eaten their body weight in cheesecake. The point is not to make it impossible to ingest calories, but to act as an extra barrier to compulsive eating. These people all agreed or volunteered to have the device fitted, so they were clearly motivated on some level.
We're talking about people who have eating disorders, who have a psychological compulsion to eat. Most of the time they may be able to control it themselves, but sometimes they might not resulting in a repeating pattern of binge eating, depression and guilt leading to more binge eating. For some of those people, having a physical barrier to stop them eating whatever they are compelled to may be all they need to stay in control.
What i think this is a better practical use for is what I mentioned above for people with those rare eating disorders where they are compelled to eat things that aren't actually food, like hair, drywall, and other non-food objects.
The disorder is called pica. And no, I think that's a terrible idea.
For one, pica is often non-psychogenic. It is a symptom of some physiological deficiency that a person isn't getting in their diet, and people with Pica are often malnourished or have comorbid eating disorders like anorexia. People with pica may enjoy or crave a certain kind of feeling or sensory feedback which they get from eating non-food items, in which case it's very important that they are able to get that feedback through other means (for example, by chewing gum or eating foods that replicate the sensation the person craves).
Above all, people with pica need to learn to meet whatever need they are meeting with pica through normal activity, which includes normal eating. Trying to restrain someone's ability to eat would be incredibly counterproductive to that person. If someone is literally trying to eat things that will harm or kill them, then the solution is for them not to be around those things, not to try and stop them eating altogether.
I mean its the same principle, keep the jaw locked shut.
It seems like the point is actually to restrict the act of chewing while having as little impact as possible on other jaw movements. Locking the jaw shut completely certainly doesn't seem like the goal.