Voice quality is insufficient

I have purchased the part under the Cyber ​​Monday Deals for just under 80 euros. Looks very neat, the keys move smoothly, to use the same, there are audible and / or visual feedback (12 LEDs around the speakers). The pairs with my Samsung GS3 was simple, I think it is just as easy with any other Bluetooth phone.

However, I will return the device after the first test, I am absolutely not satisfied with the voice quality. Although the voice was good to understand, but I found the sound to be far too dull. What also bothers me, but was not decisive: The battery is built in and the device needs to be loaded on a non detachable USB cable.