I've just returned a set of QC20's to Bose after buying them duty free in Melb.
I currently have a set of QC15's am am very happy with them, other than when I try to sleep with my head on the side, so I decided QC20's would be perfect.
After using them for a flight MEL-LAX I was totally pissed off with them. The right ear, once I got it in, was perfect! The left ear, no matter which size bud I used either would no go in without a ton of fiddling, or when it did go in and was perfect, it came out as soon as I moved my mouth to talk, yawn or whatever.
I went to the Bose store in Ontario, Calif. and the sales guy gave me another set of different buds to try (at no charge). By now, my left ear was quite sore after all the stuffing around, but 2 weeks later, I tried them again on the return leg.
Same problem!
Obviously, it is my problem with my left ear, but whatever the reason, a sore ear again on the flight home was the end, and back they went.
Melb duty free and Bose were great about it all, but I'm back to my trusty QC15's and very happy with them.