Sleep Apnea Support Group
Sleep apnea is a common sleep disorder characterized by brief interruptions of breathing during sleep. People with sleep apnea partially awaken as they struggle to breathe, but in the morning they may not be aware of sleep disturbances.

I too would be curious to hear from anyone that has tried the rig you speak of.
I started out with a mask that covered my nose but not my mouth. So I'm not sure what you use Liz.
As for keeping your mouth closed, the ad for the Pro says you can buy a chin strap for use with this.