Hate to break it to the person who wrote the article but that device doesn't check the persons pulse or any other vitals minus o2 levels in the person's body. It's a pulse oximeter. Not the most useful information to have either as having a patients pulse and blood pressure along with age/gender will provide more information for what they want to do. But in order to do that they would need to use more invasive devices.
Realistically the device itself probably worked completely fine, these things have been around for awhile and are used frequently in the medical field. The issue they most likely encountered was that it's hard to keep a dice that's gently clipped to your finger on when your being physically active, which should have been a no brainer.
Realistically they would have been better off to include a heart rate monitor to try to teach people to keep in their target heart rate while being physically active.