There's a couple dropaway rests that require no string... One of them being the Muzzy; look in the gear review forum, I did a write-up of that one over there.

Now, as far as the air-rest it seems you're asking about... click on the search feature and type in "magnet" or "air rest" and you'll find a ton of information that's already been discussed about this rest. Bottom line is that most people feel it's a ways off in development for actual usability for most people.