I use one, takes some getting use to, but, gives relief. I use it at night for 4 to 6 hrs. ( as long as I can stand it--ha!). When I was in pulmonary rehab, following pneumonia I tested high on co2, so, therefore I was put on it.
It's a non-invasive ventilator often prescribed for people who have difficulty getting rid of CO2. It's the next generation after the bi-pap, is much more efficient and can be closely calibrated to the patient, making it a much better fit for many patients than the bi-pap. Highly recommended for the right patient.