[fleetingmoments]

Yes. They're the best of the commercial trackers, at least from what I have seen. I've worked in depth on this, and we were only able to subtly improve on Fitbit's published results using more advanced models. The best models have a Kappa (measure of agreement) compared to human polysomnography scorers of around 0.6. Where 0 would be random chance and 0.8 is the agreement between different human scorers.