My husband got one about 7 years ago, and I am very thankful. He was diagnosed with moderate to severe apnea, with episodes at least once a minute. That means he would stop breathing once a minute, and his body would go into alarm mode because he would not be getting any oxygen. This is very, very bad for the human body - the amount of stress hormones the body releases when it doesn't get oxygen will destroy your system over time and can cause heart attacks.
Our insurance pays for a CPAP every 5 years, and new mask and headgear every 6 months. My husband switched from a mask that covered his nose to the nose pillows and has been happy ever since. And what a change in his personality - he's less grumpy, less depressed, and WAY less tired! (Has a lot more "energy" too, wink wink, nudge, nudge.)
edited to add:
The nose pillows are individual plastic flexible tubes, sort of corrugated, that fit onto each nostril. You can do a google search for them and find all kinds of different styles.
By the way, my husband is a mouth-breather and uses the nose pillows successfully. The air goes in through his nose and goes out his mouth. Not a problem.