Makes an amazing seal.
I wouldn't be able to sleep with only a nose connection; all the air would go out of my mouth. I have no idea how it is possible for anyone to do that. However this piece creates an amazing, solid, dependable seal with my nose and I use it for awake sessions to breathe more fully and deeply and increase my inhalation depth as part of other exercises using a different mode of my device than the one that adapts and makes choices as I'm sleeping. Of course for that I use a full-face mask that is astonishingly good - the f20. That's the first mask out of at least twenty or twenty-five that actually holds during the night even under pressure up to 25 when it ramps up that far.