Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Works well first but doesn't last

I have had the S12 for 2 years now, and although it worked flawlessly in the beginning, the quality degrades over the year to the point whereby it becomes unusable. First the channels die (there are six on the side) currently only 4 of these work. The transmit quality degrades, noise gets introduced in both transmit and receive streams and the noise gets so loud while the receiving quality gets so bad, that you can no longer use it. I like plantronics, it is the best company out there, but this product only has a shelf life of about 2 yrs. I am now shopping for another plantronics product that works.