Assuming that scientists want to find out wether an optical heart rate sports monitor has a good agreement to an established medical grade ECG system. Which device should they choose?

The Polar OH1, the Verity Sense before the firmare update, the Verity Sense after the fimware update, an Apple watch 6 or 7, one of the other 50 optical sports monitors Rob ter Horst, PhD. tested, or a future Polar OH3, which is potentially as accurate as an Apple watch 6 or 7?

Who knows? And who wants to write a new validation paper with every new sensor version, or firmware update of a sensor, which is currently said to be the most accurate sensor?