Well Whoop is nothing special at all as it tracks H/R. This actually serves a purpose for me with regards to determining that I’m either training with the correct carb/fat-inclination.
I found a video of Michael Andrew, some sort of swimmer, using it. Training With LUMEN - YouTube
Probably sponsored but who knows. It could be a great gizmo especially tracking RER.
@carytb check out the video above. That probably answers your question. You have to do a bit of calibration every time you want to use the device so I think it might be a bit of a hassle to do on the bike/while exercising. Not answering questions however is not good.