Thanks for asking, and thanks for the answer. I had been wondering about that too but it hadn't occurred to me to ask here. :)
I agree with you Freya. It feels very unnatural and unhealthy to have air forced into your nasal cavities. I've found a chin strap that actually works is the solution for me.
I have moderate sleep apnea and my blood oxygen level falls into the 70s towards the end of each 1.5 hour sleep cycle. I've haven't been able to get used to my CPAP machine and my oral appliance made me gag, so I started trying chin straps. People should know that there is one out there that is really different and it works and I'm getting much better sleep. The ones that don't work are the neoprene ones that push your jaw directly into your jaw joint. The one what works is the Knightsbridge Dual Band. (www.knightsbridgesleepapnea.com). It has two bands, an elastic and a non-elastic one, so it can be adjusted to be really comfortable. And I think most importantly it lifts the jaw from underneath, rather than pushing in from the tip of the chin. My blood oxygen now stays in the 90s. I wish I'd discovered it sooner.