Backstory: I've been using my AirFit P10 pretty successfully for the first few weeks. I initially had some mouth leakage - nothing that was really registering as a major leak, but some were waking me up. (Getting a proper chinstrap helped this for the most part.) I also had a bit of a time with the P10 "one size fits all" head strap, apparently in a different direction than most. I have a large head, and the head strap would always be too tight, regardless of how I monkeyed with the adjustments in the back.
Overall, the P10 hasn't been awful - AHIs now down to between 2 and 5 fairly consistently, but I had been reading about the AirTouch F20 and wondered if it would work better than the P10 for me - at least in these areas. (I have a full beard, and also read that the AirTouch was better than the AirFit for that as well.)
Got the F20 in, an initial short daytime trial nap seemed to confirm that the F20 might work at least as well. I also liked the way that the hose swivel and the tighter fit made turning over less of a concern.
First night ... was amazingly not good. From what I could tell from the Sleepyhead charts, about three hours into it, some leakage apparently started happening, my AirSense 10 started kicking into overdrive, leakage increased, etc., and I woke up to pressures far above what I'd ever dealt with for the P10s. Felt like someone had swapped my machine with an air hose from a garage.
After things got calmed down, I tried to get back to sleep, but it kept feeling like someone was trying to "force feed" air down my mouth (and not into my lungs). The couple of times that I was about to drift off, I was immediately awakened by the mask attempting to "inflate" my mouth. Finally decided to punt and go back to the P10 for the rest of the night. (Sleepyhead showed all sorts of AHIs before the runaway leakage, high even for a first night.)
Is this a common experience for other folks using either the F20 or a FFM in general? Maybe if someone starts out breathing through their mouth, it's less distracting? At this point, I'm not sure how the F20 is going to be useable even as a backup for me. (For the record, I had the mask settings on the AirSense 10 always consistent with the mask type.)
Helpful hint for the P10 for other "cranium-enhanced" folks: I was subsequently able to add about an inch of length to the strap by securing it with a binder clip on one end to a doorknob, then gently stretching it out and applying some gradual heat with a hairdryer. If you do this, make several small passes toward the desired length. With this adjustment and some better luck with the mouth leaks, the P10 is working even better than before.