Per Chinavasion's web page:
"The durable composite resin filling is designed to fit in a hole 2.2mm in diameter and 1.7 mm deep and will pick up sound and vibrations from your mouth to produce incredibly clear sound.. never forget your trusty bluetooth kit ever again, simply install and forget".
It's a unique concept, that's for sure. This mandible-to-microphone technology's been around a while, and works very, very well.
(E.G. Aliph's Jawbone headset).
Are we seeing the future of microphones .. ?