Sound quality is very good, with sufficient bass for my needs. But, as I only listen to MP3s, I can't claim to have given the audio quality a thorough test.
Noise cancellation is excellent, greatly reducing any repetitive noise, e.g., air conditioning fan nose, road noise, airplane cabin noise, etc. The instruction manual recommends that you don't use them whilst driving though, as the noise cancellation really does isolate you from the driving experience. However, when used in a car the sound is so much clearer that you wonder how you managed before!
Unsurprisingly Bluetooth connectivity works fine with my Nokia phone, but it also connects fine with the two dongles that I use.
Unfortunately it doesn't connect with my Siemens SL565 cordless phone, but I suspect that is due to the Siemens rather than the headset.
The sound over Bluetooth is definitely comparable to when used over a wired connection.
Can connect as both a headset and as stereo headphones simultaneously, so you could be listening to music from your PC and be connected as a headset to your mobile at the same time. Even if you're using a wired connection and you're not connected to the phone, connecting to the phone is simple, just remove the wire from the headphones and hold down the power key for a couple of seconds. You can then answer a call using the same key and enjoy a conversation where the noise cancellation makes it much less effort to hear the caller talking.
Quite comfortable to wear for most of the day, although they do feel a bit heavy on the top of the head after a few hours of wearing.
The manual says that the rechargable attery will last for 40 hours using just the noise cancellation and over 12 hours of using bluetooth. I haven't used the bluetooth heavily yet, but the noise cancellation figure appears to be about right.
Will only pair using the PIN "0000", so would not work with devices that have a fixed PIN that is not "0000", e.g., some bluetooth transmitters.
All in all, very pleased with them.