There is a wonderful channel "Quantified Scientist" (https://www.robterhorst.com/, mostly YT content) with benchmarks of smartwatches and trackers against EEG and more profesional heart monitors. It would be interesting if he could benchmark WiFi as well.
AS, in short, it is easy to measure pulse or sleep somehow. It is hard to measure it well consistently (pulse when someone is running, biking or weightlifting, sleep when people sleep with others, move, etc - or lay sleepless).