I've used the First Class Sleeper on overnight flights from NY to Santiago on LAN and really liked it. I'm only 5'1", though. It's true, you must not over-inflate. However, on a trip last week to Munich, I never attempted to use it. The Lufthansa seats in coach felt too narrow to lay the thing out comfortably and when the person in the row in front reclined his seat, I was squashed and unable to scrunch down the way the instructions tell you to.

I think one's height has something to do with it. I'm 6'0" and even with sitting in United's E+ seating it put my knees too far forward. I tried letting air out a bit at a time and it didn't help.

I've never understood these products. Do you really need more support in your seats? Do you really want to reduce your legroom by yet another 2"? If anything I would prefer to scoop OUT the headrest so that I can lean my head back further. Not push myself forward.