Basically they are a biofeedback device used to determine breathing and heart rate and monitoring the balance of the autonomic nervous system. I believe it can be a very powerful tool to develop the skills to maintaining and/or creating an increased parasympathetic tone. Breathing techniques by way of the respiratory sinus arrythmia can be very effective at improving ANS function.
We've advised the ladies to practice with them at least 3-4 times per day for around 10 minutes, if not more often. We'll be collecting some rough data. I hope to get more athletes hooked up with them in the near future.