Bet you never expected all the replies, especailly for a very fair question -
I've been diving almost 30 years, and while its neat technology, I never saw the need, not because its "dangerous" but because of the cost.
Unless you have a real desire to have the latest and the greatest (someone spent 20k++ to have the 1st plasma 60" TV), are super technically oriented - and willing to do the maintenance required, or are a serious photog wanting to virtually eliminate bubbles - these may not be the breathing devise for you. And I realize your question was "what are these things", not that you are planning to buy one.
I don't think they are for the average diver, and certainly not for a beginner. The inital usage was military - mission critical when stealth was needed.
That said, I would consider one if the maintenance issues and pricing could be "solved" - until then about as technical as I'm likely to get is a 119 steel w/ 36 o2!
Good luck and welcome to the board.