Summary: The Plantronics K100 delivers great-sounding, hands-free calling on both ends of the line, and its FM transmitter is a nice bonus when it works, but look elsewhere if your phone is one of the few that don't support voice-activated dialing.
Pros: The Plantronics K100 features a dual-microphone setup that aids in echo cancellation, and a loud, clear internal speaker. A built-in FM transmitter combines with A2DP support to enable the K100 to serve as a Bluetooth-to-FM bridge between a smartphone and a car stereo for audio playback.
Cons: The K100 doesn't feature a dialing system or internal phonebook, so it doesn't play well with phones that don't feature voice command systems of their own.
Excerpt: The K100 is a hand-free Bluetooth kit for in-car use. It has a large metal clip on the rear to hook over a sun visor and comes with a USB cigarette lighter adaptor and micro USB cable for power. It's easy to pair with a Bluetooth phone - our iPhone 4 connected automatically as soon as the K100 appeared in the devices list. There are dual microphones on the top edge which help eliminate echoes. In our testing, this worked well, and the speaker proved loud and clear.