The long of the short of it: Sleep trackers do not work.
Not even the most expensive ones you can buy work. They are exceptionally limited devices that only measure when you are moving or not8. As an insomniac, I’m sure you’ve laid completely still for hours at a time yet remained wide awake. A sleep tracker would record that as sleep. Conversely, it might record that you’re awake when you’re in fact sleeping, especially during lighter phases of sleep where you do move more.
If you are actually interested to see how you are sleeping, it’s best to participate in a sleep study where they can record your brain waves. It’s certainly a more complete set of data that can help you understand where you are with sleep better than a commercial watch ever could.