Sleep trackers do not actually measure sleep or see how well people sleep, but rather estimate sleep by looking at inactivity levels. A tracker gives insights to your sleep patterns, but for more accurate data about those patterns you would have to complete an actual sleep study.
If you are a healthy individual who just wants some awareness into your habits, a tracker may be a good tool for you, however, if you have any concerns about your sleep, you should talk to your doctor. The good news is that with so many sleep trackers on the market, there are many different price points, so almost anyone can find a tracker within their budget and preferences.