Pros: great sound, effective noise cancelling, portable
Cons: braided cable causes cable noise
The AKG K490 NC (noise cancelling) headphones offer great sound, great style, and noise cancelling at an affordable price. To my ears the sound does not change when NC is turned on/off. The background noise just fades away. If you are listening to an audio source when you turn noise cancelling on, the source is muted until noise cancelling is up and running - about one second or so. Then the difference in sound is like stepping into a quiet lounge from a busy street, and being able to hear every nuance in the music without the outside rumble.
I haven't seen any bad quality issues in my copy. The major complaint I've heard is that the extending band breaks just before the hinge with any pressure placed on it. As I've posted in these forums before, the band has been redesigned and now incorporates a metal reinforcement band, so it's not all plastic anymore. I use these headphones daily at work, wear them on the walk home, wear them at home, wear them walking the dog, and I even took them on a one month Europe trip where they were squeezed into my backpack the whole time (I only used them on the plane). There are no signs of stress on the band nor the hinge.
While I like the flexibility of braided cables, and I prefer this cable to rubber ones, the cable noise is very audible when it rubs on my clothes. It's a trade-off I'm happy to make. The cable is completely removable, and in order to charge the battery (for the NC function), you use the same headphone port for battery charging. If Noise Cancelling fails, and you want it, you can't charge the battery and use the headphones at the same time.
These headphones come with a clam shaped soft case, an airline audio adapter (ancient technology these days as most airlines have switched to 1/8" stereo audio ports), a USB to micro stereo plug (3/32?) for charging, and a 1/8 mini stereo to micro stereo plug to provide audio to the headphones.
The headphones do not give any audible indication that the batteries are fading, but you do hear background noise increase, so I guess that's an audible warning. The power indicator light on the backside of the left speaker is part of the on/off switch, and changes from green to red when the battery is weak, and then back to green again as you charge the battery.
Right now these are my favorite headphones. I have other great sounding phones, but some are too bulky while others are Bluetooth and portable but don't have noise cancelling. Right now I'll take noise cancelling over wireless any day. The only thing that would make them better is adding Bluetooth.