I've been using this for months after I lost my plantronics 640. I like the size and look alot. At first, it seemed uncomfortable compared to the 640 which was very comfortable. Now, I would say it's not bad. I don't notice it too much when it's in my ear.Sound quality is good, about the same as the 640. Functionality, it's easy to answer and hang up on calls, but using features such as redail is almost impossible as holding it a second too long will turn off the device.Battery life is about 2 days with moderate conversation.