By all means don't use those things if they are old, just used mines, and they were stored in the plane for about four years, it's really complicated to hold on to it for the rest of the flight if for whatever reason the liquid doesn't get converted into gel or solid as it's suposed to... yes you guessed it, it doesn't always work I CAN tell you about it. My wife wasn't too happy about holding it either, thank god we improvised a couple of bags and hanged the package to the small hanger thing on the rear seats.

I am going back to the old trustable milk bottle...

Regards,

Ignacio

BTW: I never new if the things worked when new, because never tries them.