Good to know, and not surprising to me as I've had a Garmin Forerunner for about five years. Its chest strap could read my HR no matter what, and was dependable whether I was just our for a jog, doing yoga, or doing Super-High Intensity Training ("****" workout... heh!).As for accuracy, it was the most reliable reading I've had during exercise yet. Much better and accurate then either the Apple watch itself or my old Fitbit.
The old Forerunner could never get a HR without the strap, of course. At least the AW has the option.
Enjoy the extra accuracy, and let us know how much battery life it saves, too. I've heard that the Bluetooth connection uses less power than keeping the LEDs turned on all the time.