I'll make it short. My counterpart hears me very well and also has little fault the sound. This is consistent with the other product meetings here. Unfortunately, the device can be extremely loud. And even on the quietest level (the headset then makes an announcement that it has reached the minimum volume) does it really hurt. In an office environment because I fear for my hearing. Was used an iPhone with iOS 6 8.1.x.
The device I've missed the latest firmware v28. Delivered it was with such ancient firmware that not even wanted to communicate App for iOS with the Plantronics. After an update it went. The app is quite carelessly, but then offers all the setting (HD Voice we need for example only manually activate). And they will probably also need not too often follow when everything is adjusted.