I couldn't use open headphones on a flight, the whole point is to cover noise from the plane and other passengers. Good quality noise cancellation is a must for me now. I was ambivalent that it would be any better than regular headphones would be when I first got some, but I wouldn't fly without now.
Ah fair enough - for me, I'm only really on short 2.5 hour flights, so for me it's simply to be able to listen to some music, or watch a downloaded tv program/film off a tablet, for that purpose it works fine.
As I am also a cheapskate on these flights, I try and get away with the tiny 'free' carry on bags, and I suspect even with vacuum bags for other things, I wouldn't really have the space for headphones, though I suppose you could leave them round your neck/on your head.
If I was on a 12hr+ flight, I probably would to look to use bigger headphones.