I used my Mach I for about three trips before I gave up on it and sold it on E-Bay. The light weight was nice, but that was the only positive for me. I had a hard time getting the earpiece to stay in a position where I could hear correctly, regardless of which insert I used. It took WAY too long to get untangled, inserted, clipped on, etc. Also, because I fly corporate type aircraft, every time a passenger would try to say something I needed to hear, I'd have to take the earpiece out, then refit it again once the conversation was over. PITA for me.

After I gave up on the Mach I, I bought a set of Bose QC-2's and the boom mic adapter from UFlyMike.com. It's about $500 for the whole thing, and you get essentially the same thing you would get buying the Bose X, at $1000, but lighter and more comfortable. The noise cancellation is nice, very light and comfortable, no complaints at all. The boom still allows you to plug in an MP3 player, or in my case, a portable XM receiver. I also use the QC-2 standalone when I'm flying deadhead to reduce noise or want to listen to music in the hotel room. The batteries usually last me for a whole 7-day trip.

-NTFB