For me the sound quality is by far the most important factor when I compare headsets. Everything else is secondary. I drive a very noisy construction van so background noise is a serious problem. I have compared 8 different headsets and the Plantronics Voyager 510 is the only one that allows a clear conversation in this environment. I have used it daily for over 2 years and often for 6+ hours straight until the battery is dead. In a loud, dirty, construction environment, often lying on the ground, it's the only thing I've found that works. With the other models, either I, the caller, or both of us couldn't understand a word being said. For those of you that don't have background noise issues, I can add that even in quiet settings this unit has better sound quality than all the others that I tested. The way that I do my tests is to pair 2 headsets, put one in each ear and then switch between them while on the same call. This way I and the caller can compare the sound quality at almost the exact same time. The 2 cons I can mention are that the on/off button is too small and hard to push, and that when the battery is almost dead the buttons stop working (even though the sound continues fine) so you have to hang up using the phone instead of the headset. To be fair though, the "almost dead battery" symptoms happen in many of the other ones I've tested also. I don't care, sound is everything.