Contrary to what is written in the title, this is an electret.
It is used in many acoustic recording. It has different "grid" that alter its characteristics in terms of frequency response in and off-axis. An accessory can also change its directionality.

OVERALL OPINION

As it was said, it is absolutely sublime. Nothing comes close to him. Purity, cleanliness and a spectral width and dynamic! This is priceless, but when we heard, we attack the bank next door to be able to pay it, not one but two.
In addition, the simplicity of its design gives it a pro foolproof. For my part, I have a pair comes in a bag securely and with various accessories (including a stereo bar). As I said, it's expensive, but the price is good value because there is no competition ...