Instruct: Classify Amazon reviews into positive or negative sentiment
Query: It's great while it works...

...and then it falls apart. Bought the unit, had it less than a month, had it replaced and still no joy. The basic problem is that while the sound quality on hearing your caller was always superb, the volume with which the other party can hear you worked fine then diminished to a whisper--and no amount of fiddling with the microphone position or warranty repair could correct the problem. Additionally, the ergonomics of the unit (considering that the mic has to be practically IN your mouth to work when it worked at all) are very wonky. In the first few weeks while the unit was working properly, I still ended up wrapping the cord up and over my other ear (as I used to do with my freebie earbud hands free) to stabilize it. Overall I can say that I am a HUGE supporter of the noise cancelling technology they are pioneering, but that this product is an equally HUGE disappointment.