I completely disagree with bblkk on trhe dental school equipment and implying that j hooks are a lesser form of treatment than a facebow. Some orthos only use j hooks and the companies that make dental equipment want to have their latest products right in front of those future orthos who will buy what they are familiar with.
As to silvers questions my experience is 20 years out of date (my youngest daughter) and my personal experience is about 55 years out of date. That said I spent a lot of time in headgear doing the 14 hours a day thing. My ortho always wanted me to wear it more, and I was one of his few obedient patients, aided by my parents. Headgear could not have been more embarassing at the time, you will have to trust me on that and my friends did not even wear theirs when sleeping, yet they ended up with straight teeth. When the issue came up with my daughter the reqirements of headgear use was down to 8-10 hours a night. I still hated the thought but her best friend had j hooks so she did not mind. That amazed me but she did her entire time with that on every night for the 18 months of treatment.
With me, a more difficult case with a more adversarial patient, I wanted to know exactly when I could stop wearing the thing. My ortho tried to convince me, and my parents, that I should keep wearing it, at night only, for the duration. That did not happen. A girl I knew in college wore a cervical headgear along with her retainer, the only two bands in her mouth were for the facebow. My point is the orthos seem to use it for more than just brute force at the beginning but finding patients willing to live with headgear in the first place, then for two to three years of treatment, and then into retention rarely happened 50 years ago, 20 years ago, or now. Outside of my daughter, I have not seen anyone, at any age wearing headgear in public in 25 years. If not for people wearing them in videos and posting, no one would know what they were. I never did understand why people who would never wear headgear in public will show their headgear to anyone on youtube.