Of course, whenever you introduce active noise canceling to a headphone -- and all the digital processing it brings with it -- you tend to lose a little bit of sound quality. Noise-canceling headphones usually don't sound as clean or clear as "passive" headphones, and some introduce a faint hiss (though with the QC20s that hiss is very minimal). In other words, if you value sound quality above anything else, you probably shouldn't get a pair of noise-canceling headphones, and from a sound quality standpoint, the QC20s don't measure up to many in-ear models in the $300 price range. This just isn't a headphone that's so good that you'd want to go back and listen to your whole music collection just to experience how it sounds with all your favorite tunes.
But even though I have other, better-sounding headphones at my disposal, I still found myself gravitating toward using the QC20 as an everyday headphone because of how comfortable it was and how it managed to muffle a lot of the New York street noise.
I also tested it on a plane ride to Seattle, and while I thought the overall noise reduction on the QC15 was slightly better, the QC20 was more comfortable, and its in-ear, earbud-style design is good for sleeping because you can rest your head against a pillow or headrest without having your headphones getting in the way. However, you could argue that going smaller has one potential drawback: you may be more likely to lose the QC20s than a full-size pair. Then again, I have known people who've left plenty of larger items in seat pockets on planes, including iPads and QC15s.
OK, now for the downsides, and they all involve the battery pack and control pod on the cord. First off, it's a little awkward to have the battery pack dangling from your headphone. It's also worth noting that the battery isn't replaceable, so once it peters out -- and someday it will -- you're basically left with an MIE2i headphone with a dongle attached to it. When I asked Bose about that, I got this detailed answer:
The lithium ion battery is not replaceable. The battery is expected to maintain its full capacity (16 hours of customer use per charge) through 500 charging cycles. For a heavy user who charges roughly every 2-3 days, this would be equal to about 3 years of use. After 500 charging cycles, the battery will continue to recharge and operate the headphone, but the capacity would be reduced. This deterioration in capacity is common to all lithium ion batteries.
Lastly, if you forget to turn off the noise cancellation, which I did a few times, you'll end up with a dead battery overnight. For this price, there would ideally be some sort of automatic shut-off feature when the headphones aren't in use.
Despite those drawbacks, I liked the Bose QC20s a lot. Their sound may not measure up to what you get from competing $300 in-ear headphones, but they sound good, are very comfortable to wear, and offer excellent noise cancellation. They also take up very little room in your bag.
A lot of people will think they're overpriced, and they'd be right to think that. But for a certain subset of the headphone-buying population, the QC20s are an excellent product that's strongly worth considering.
For instance, if you're a frequent traveler who doesn't want to carry around a larger over-the-ear model like the QuietComfort 15 or Beats Studio 2013 (which sounds better than the QC15, but the noise-canceling isn't as good), the QC20 is a tempting alternative. It's also a good choice for someone who's looking for a strong noise-canceling headphone but doesn't like wearing full-size headphones.
Just be aware that because of the lifespan of the integrated lithium ion battery, that noise cancellation won't work forever. If you're OK with that and don't mind their hefty price tag, I have no problem recommending the QC20s.