And it trains you to not sleep on the back. It is a device therapy. Some people like devices because they are easy and simple. You put it in your mouth, you wear it, you wake up in the morning, you take it out. The difficulty is that it takes time to get used to a device like this.
Some people drool a lot.
Some people have muscle soreness when they wake up in the morning. So, I do fit people with oral appliances if they prefer not to have a more permanent surgical treatment. I offer the oral appliance to my patients and I would say most of them prefer to get a more permanent fix rather than wear an appliance forever.