Many have already pointed that there have been studies to measure the accuracy of sleep analysis by wearables. They aren't that great. If you have a concern, you should definitely seek out a polysomnograph, and wearables should not be a replacement for that. However, you can't get a polysomnograph every night, and wearables are probably the best option for regular analysis. Just because they're not that great doesn't mean they're useless, and doesn't mean they won't improve.