Duly shaken. $15 is a bargain for a glass.
I understand they don't age further once bottled...which is unlike wines...how about cognac, I always thought that continued to age...
I too have been known to pick up a good bottle from duty free for trip...
BTW, I find the LHR Duty Free scotch selection and prices to be truly outstanding for an airport...which reminds me, I think last time I was there I got my grandfather a Ballentine 25 (he drinks the regular Ballentine) and I doubt he has even touched it (a waste in retrospect)...