The peak flow meter measures the airflow through the bronchi and thus the degree of obstruction in the airways. Readings from a peak flow meter can help one to recognize early changes that may be signs of worsening asthma. The breather however, is a Respiratory Muscle Training (RMT) device. It is a resistive type of device meant to strengthen your respiratory muscles. In the same way that a person lifts weights (resistance) to build skeletal muscles (like biceps) this device has pressure settings so you inhale and exhale against pressure (resistance). When you do that you are engaging and strengthening all of your respiratory muscles.
Research has shown that respiratory muscle training (RMT) improves respiratory muscle strength. Children and adults suffering from asthma should benefit from using the Breather by being able to clear the airways more efficiently due to increased expiratory muscle strength. RMT also reduces the frequency of asthma attacks, severity and frequency of diurnal and nocturnal symptoms and perception of dyspnea. Regular RMT by using the Breather should result in reduced need for the use of your rescue bronchodilator for instance. You may find the following articles interesting: https://www.pnmedical.com/?s=asthma and please do let us know if you have any questions.