Good sound quality, good fit is short-lived,
This review is from: Plantronics Discovery 640 Bluetooth Cell Phone Headset (Wireless Phone Accessory)
The sound quality of this unit is good enough for my needs, though the volume does not go as low as I'd like sometimes when the other party is very loud.
My major gripe is that with the proper sized earpiece, the unit rotates so that it hangs straight down making my voice muffled to the other party. Adding the optional ear loop works OK but this setup tends to fall apart very easily. I think the reality is that for good stability you need the ear loop, but again, the thing tends to fall apart too easily (not break mind you but the earpiece falls off allowing the ear loop to also fall off).
I will look for a more stable solution in the future.