Like the QuietComfort 2s, the C820s headphones feature an over-the-ear (circumaural) design and soft, cushioned earpieces that effectively seal off your ears from a noisy environment. The Jabra headphones offer the same fold-flat design of the QuietComfort 2 and have noise-canceling circuitry that's built into the headphones themselves, rather than having a little box incorporated into the cord. They also come with a protective carrying case and a two-prong adapter for plane travel, as well as an extra bit of cord that extends the length of the headphones' cord. That main cord is detachable from the headphones, so you can use the headphones to simply hush noise (say, while you're riding on your lawnmower) without the hassle of dangling cables.
The long and short of it is that these two headphones are very similar. But here's the deal: the Jabra headphones just aren't quite as good. They're comfortable headphones, but not quite as comfortable as the QuietComfort 2. Their noise cancelation is effective, but it's a tad less effective than that of the QuietComfort 2. They sound good--but, again, not quite as good as the QuietComfort 2.
Now, the QuietComfort 2 aren't the best-sounding headphones we've heard, especially at their lofty $300 price, but they do sound richer and more refined than the Jabra headphones and their bass packs more oomph. Jabra's bass is decent enough, but on bass-heavy tracks, such as Snoop Dogg's "Drop It Like It's Hot," you can really sense that the Bose's bass is fuller and a little tighter.
That said, the one thing you can do with the Jabra that you can't with the Bose is listen to music and movies when the noise cancelation is turned off (or when the AAA battery that powers the noise cancelation dies). The sound is definitely a little muffled when the noise cancelation is off (when you turn it on, the volume is automatically boosted), but we were able to watch--and listen to--an episode of The Office on our video iPod without any trouble.
What's it all add up to? Well, despite failing to measure up to the model it chooses to imitate, the C820s gets most of the way there for a fraction of the cost. In other words, if you're looking for the poor man's Bose, this is it.