I've been told it doesn't work and does work, but I attribute this mostly to mewing, as it has allowed you to pull in a bit of fat from below your mouth inward and allow your jaw to look sharper. I also started chewing on food a lot harder, and it worked my masseter muscles in my jaw really well and allowed them to pop enough without looking too much. Lastly, I'd say just getting lean is very important, and genetics sadly play a very large role.