They use alloy metal tweeters.
As far as sound, well, they measure and are built to the standards that you would expect from speakers that cost 4-6x the price. Literally. They have some phenomenal measured performance. But you do need to cross them at 80Hz or higher and keep bass from them. They were not designed to play bass, but instead to act as high quality mid-treble modules.
With some minor modifications you can increase their SQ by a fair margin. These mods are just basic things that most manufacturers overlook for mass production. I can describe them if you desire.
-Chris