After spending some time with the Bluetrek Crescendo Voice and the Jawbone Icon, going back to a standard bluetooth headset is a little bit disappointing. But the Bluetrek Duo Stereo is not a standard headset. It might fool you into think it is one, but when you see the headphone adapter in the box, you know it must be special. The Bluetrek Duo has A2DP as its specialty– and it (unlike the Jawbone Icon which also has A2DP) has the ability to be used with a set of headphones.
In all honesty, the Bluetrek Duo is simply an OK bluetooth device by itself. It doesn't offer noise cancellation, an app store, or any other fancy features. But that's OK, since most people only need those features once in a while. With a simple pairing to my iPhone, I was immediately enjoying A2DP stereo audio. Without the adapter plugged in, the Duo acts like the Jawbone by playing the music through its own speaker in mono. When you plug the adapter in with your headphones, the signal is moved to the headphone port and it sounds almost exactly like if you were plugged into your phone natively.
The bundled earbuds are actually decent for the price of the bluetooth headset, similar to a pair of cheap Sony Fontopia in ear headphones. They aren't great, but they are definitely decent for the consumer. They include a clip so they and the Duo can be worn as a necklace clipped behind your neck. This is very convenient as the adapter also includes a built in microphone allowing you to talk on the phone.
My only problem with the Duo is that for some unknown reason, on the iPhone (and maybe other phones), the two channels of music are flipped. This is very noticeable in songs such as the Red Hot Chili Peppers' Dani California and the Foo Fighter's Come Back, where there are clear differences between the channels. This could be remedied by a firmware update or just swapping your earbuds or flipping your headphones around.
Overall the sound quality is decent. It isn't quite as good as plugging directly into the phone, but the fact that you can move 30 feet away from the phone makes it very convenient. You could pair to your computer and have a set of wireless headphones too. I think it's a neat device and if you want to convert your current headphones to wireless, this is a great option. If you just want a good headset for driving, stick to the Crescendo Voice or Jawbone Icon.