The bose-x is worth every penny. 6hr+ flights and it's barely noticed. I have four of them; three converted to aircraft power, and one with the normal jacks which I can use in other planes.
The main drawback is that you need to carefully brief passengers that they cost more than 20 quid and to treat them with care! This suprises a lot of people. They have to be looked after; they are not cheap club headsets which can be kicked around.
Bose are raking in the money on these, but so is everybody else in this business, selling yoke clocks for £1000, £300 GPSs for £3000-£7000, altimeters for £3000, etc.