AKG K490 NC - Reviews
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.
Pros: Good sound and comfort
Cons: Fatal Design Flaw
I got these phones as a gift, and I am quite happy with the sound quality and comfort. The noise cancelling is also quite good, and can completely eliminate certain frequencies of extraneous noise. Fun playing with the on/off switch to appreciate the difference! I listen to a wide variety of rock and old school 60s jazz, and the phones are quite good for this kind of music. Pad pressure on the ears is about perfect for me, and the pads themselves are comfortable.
But there's one killer here- the post that attaches the earpiece to the band can easily snap off, and there's no way to fix them. Mine broke, and when I mentioned their delicacy on an Amazon review, I got several other owners chiming in with the same issue. If you nag AKG enough, they WILL replace it with a fresh set. They did it for me, and an Amazon customer thanked me for giving him the scoop.
But AKG KNOWS this product has a design flaw. So they just replace it on an ad hoc basis to anyone who complains insistently on replacement. Despite being NCs, these are FAR too delicate to travel with. So you take your chances with what is otherwise a satisfying phone.
I had the K495 (unsure as to the difference between the two models, so apologies if irrelevant) and - to my way of reckoning, there is an even bigger flaw than that that you mention...

The left earpiece (where the electronics are held) has too much vacuum against the ear, and - whenever you put them on your head, you can hear the driver compress / crackle - after a few times of that happening, there was quite a major loss of treble / high end on the first pair that I had - and the second (replacement) pair I had sounded bad right out of the box - again, on the left side only...

AKG really should've thought about this design just a little bit more before pushing it to market!
I wonder how these compare to the Bose noise cancelling headphones. Please, if anyone has any experience with both of these, let me know and with enough details to make an informed decision or opinion.