One thing I didn't love: the headphones are charged via a jack on the left earcup using a non-standard USB cable (you get up to 12 hours of battery life from a single charge). It works well, but the problem is that if you lose the cable, you won't be able to charge the headphones (you can't just use the Micro-USB that comes with a lot of phones and other devices). I therefore suggest keeping the cable stowed in the inner pocket of the carrying case for safekeeping.
Finally, if you want to make maximize the sound quality of the headphones, they have a detachable cord (it plugs into the jack I just mentioned) that allows you to use the BTs as wired headphones. I suspect the vast majority of people won't bother using them that way (after all, why buy a wireless headphone if you're not going to use it as a wireless headphone?), but the wired option is there, which is good.
The big problem with Bluetooth headphones is that they have a tendency to sound a little muddy and fail to deliver crisp, clear sound. In the last year, several higher-end Bluetooth headphone managed to overcome that problem, delivering a sound more like wired headphones. The Harman BT joins that group of very good-sounding Bluetooth headphones.
Like the NC, the BT sounds comparatively natural and accurate. It has a sound profile similar to that of the CL, which is considered a balanced, more neutral set of headphones that doesn't overaccentuate the bass or treble. Still, like that model, the bass here is plump and pleasant (it seems to be a touch more plump than the CL's) but not overreaching. As with the CL, there's a bit of restraint in the treble, so you're not going to get that edgier detail of "faster," more aggressive headphones that push the treble harder. I wouldn't call these laid-back, but they're fairly warm. I tried them with a variety of music and came away feeling that they were quite versatile.
For instance, the Black Keys' bass-heavy "Everlasting Light" held together well. With lesser headphones, the bass line can come across as mushy, but with the BTs, it had some decent snap to it. Yeah, you're going to get a little more detailed, open sound and a bit better bass from a wired headphone such as the Audio-Technica ATH-M50. But for a Bluetooth headphone, the BT offers very respectable sound.
I thought it was neck-and-neck with the Parrot Zik and Nokia Purity Pro by Monster for sound quality. But I did think the Zik was a little more comfortable to wear.
As a headset, I found the call quality to be quite good. Indoors, callers said that I sounded clear and didn't sound like I was on headset or speakerphone. However, it's worth mentioning that, as with a lot of headphones that have the mic placed on the earcup (and not so close to your mouth), if you're in a noisier environment or there's some wind blowing as you're making a call, people may not hear you as clearly.
The Harman Kardon BT offers excellent sound quality for a pair of Bluetooth headphones, with an impressive fit and finish. Like with the NC, my only reservations about them concern their design. While it's distinct and eye-catching, it won't appeal to everyone, and the headphones will seem heavy to some folks. While I found the Harman BT comfortable, I suspect that some people won't be totally enamored of its fit.
In an ideal world, of course, you'd get a chance to try these before you buy them and compare them with competing products. The alternative is to try them and return if you don't like them (stores like Amazon and Crutchfield have a window to return the products without incurring a restocking fee). I think most folks will like them a lot, but each person's ears and head are different, so there are no guarantees. Still, as far as premium Bluetooth headphones go, the Harman Kardon BT is one of the top models available today and is comparatively well priced at less than $250 online.