The main purpose for manufacturing this portable oxygen concentrator is to allow free movement of oxygen dependent people. It provides the longest battery time, i.e. 4 hours due to which Respironics evergo oxygen concentrator has a clear edge over other companies. The output of oxygen is 1050 ml per minute. The device weighs only 10 pounds and it is equipped with a touch screen facility which allows you to monitor your therapy and adjusts settings without having to go to the hospital. Its incredible non-medical design makes it look more like a carry-on bag. Hence, you ought to trust this oxygen concentrator because it is completely reliable.