Essentially the sensor capacity for all of them are similar, with the Apple Watch slightly better than many of the competitors, the form factor for the oura is best. We make an algorithm that runs on many of the devices using Sonic Sleep and we found that our algorithm on Apple Watch performs the best. The oura is good too for sleep wake. Biostrap is good for SpO2. You can also buy a pulse ox that is less consumer friendly but accurate.
But DO NOT put too much value in the sleep staging. Current state of the are is bad at this.
Daniel Gartenberg, PhD
With such devices, is there a hope of portable EEG based sleep monitors?