I have been cpap user for only 3 months. I started with the nasal mask, but I would take it off at night in my sleep. I kept at it for a month, but then I switched to a full face mask, which stays on all night. The differences that I noticed (at least for me) are that the Full mask seems to lose its seal easier when you move around in your sleep, and the Nasal mask seems to give a more concentrated and direct line of air pressure since it goes down the nasal passage (if you are not congested).
Unfortunately, as soon as you open your mouth with a Nasal mask, the vacuum effect happens for a second and that concentrated air pressure comes right out...
Why don't more people use a full face mask?
Many good comments here. Essentially, what it all boils down to is "whatever works for you". I'm glad you found an interface that works for you! In my case, I have a thick beard and moustache, so no full face mask seals well enough for me. I use and really like the Breeze. YMMV. I have an Oracle in the drawer for emergency use if I have a heavy cold.
Getting old doesn't make you 'forgetful'. Having too damn many things to remember makes you 'forgetful'.