I recently upgraded from an old ResMed S9 to a ResMed Airsense S11. At the same time I upgraded from the old ResMed Mirage Activa LT Nasal CPAP to the new ResMed Airfit N20 CPAP mask. Initially I purchased the N20 large, because my old Activa was a large. That was a mistake. after using the fitting kit that came with the N20, I quickly worked out that I need the Medium or possibly the Small N20. Anyway, Respect Health were great and swapped the N20 Large for the N20 Medium. Massive improvement in comfort. Not too tight. No leaks with the Medium, whereas the Large had to be stretched so tight, to stay on and not leak, that it was uncomfortable.

I think the N20 is great. There is one difference in design between the N20 and Activa. The Activa had a baffle or deflector of sorts that directed air flow down towards the chest of the CPAP user. The N20 does not. Airflow is directed straight outwards. My partner, now gets blasted by airflow. She finds the ResMed S11 much quieter than the old S9, but finds the rush of air from the N20 to be annoying. Maybe ResMed need an "N21" with a feature (baffle) from the Activa.