My wife and I would disagree. I didn't realize but there's something she said to me when we debarked: for once the seat fabric didn't SCRATCH our skin has hell during the flight. Plus, I do find they provide an inch of additional comfort. Reasonable expectation being, these are not five-stars-deluxe-beds by any means, just something nice.

FWIW I installed them as soon as we boarded (once thank, credits to my wife for this idea). Even when sitting the feeling is very good (and need I remind, you do no longer touch the seat fabric).