First off, I don't understand the logic as to why anyone would want to go through all the grief of wearing chin straps and/or tape on their mouth and then having to hold your tongue in a certain position (and to always face West) while you sleep or other extremes when the simple problem of breathing through the mouth is easily remedied with a properly fitted Full Face Mask.
I've owned exactly 1 FFM I've been using for over 4 1/2 years and I've never had a problem with it sealing against my face, so, exactly how would I benefit from trying to force myself to not open my mouth when I'm asleep? How much greater would my CPAP therapy be if it were being delivered through either a nasal mask or nasal pillows that I'm not already getting through my FFM?
I actually received a brand new Swift FX for free when I bought my S9, I tried it for a couple of hours but I woke-up gasping for air through my mouth, so I tossed the Swift into the garbage and grabbed my Mirage Quattro - switched the mask type back to FFM on the S9 and went back to sleep. All it did was to create a problem and I'll never do it again, there's absolutely no reason good enough to make me want to put myself through that experience again, after 4 1/2 years on CPAP I've determined that I really like breathing whenever I sleep, and anything less than a FFM will not consistently allow me to do so.
I have been breathing and snoring loudly through my mouth since I was around 5 years old (according to my parents), so what would I gain from going through all the grief that others have to do just to force myself to breathe through my nose? I don't understand the obsession to try and "convert" anyone here that's already receiving proper therapy while wearing their FFM? Isn't the whole idea to find a mask that fits and to wear it?
One big positive benefit that I've gained since getting my S9 with ClimateLine hose is the ability to run the humidity really high without rainout, this in turn has made my sinus and allergy problems virtually disappear for the first time in my life. The secondary benefit is that now I can actually breathe much more through my nose while sleeping than I ever have but, for unknown reasons, I still sometimes wake-up breathing through my mouth while my sinuses are completely open. For most of my life, I've HAD to breathe through my mouth, sometimes for days or weeks (literally) because of allergies, not to mention a deviated septum doesn't help, so there's a good chance that a few other CPAP users have these same considerations taken into account when they're selecting whichever mask type they want to try first or second etc.
One of the biggest problems in my opinion is caused by a lack of education on proper mask usage, like washing the mask cushion and their face, then there's the strap tightness issues, either too much or not enough, I suspect a lot of people might have a bigger problem with their bed pillow causing their mask to shift while sleeping on their side and causing their leak problems.
Lastly, being a SCUBA diver, we're taught to get used to breathing through our mouth since our face mask covers the nose, I was already used to it thanks to allergies but, I've seen new divers try to panic when they can't breathe-in through their nose even though they've got a regulator in their mouth and a full tank of O2 on their back, fortunately for them, that's what open water class is for.
I'm not advocating for any particular mask type other than what works the best for someone and is the easiest to use, especially for a brand new CPAP user, they just need to try and get used to their new equipment and how to properly use it which is a LOT to get used to at first, if they're a known mouth breather and they have a FFM, they only have to worry about possible mask leaks and not mouth leaks. I think a good RT would rather help a new user to get used to using their CPAP first before they made them start jumping through all the hoops required to only breathe through their nose.