Wasn’t nearly as bad as I expected. If you think of the codes as meaningless IDs, there are no problems. The system is unambiguous which is the most important thing. MEL refers to one specific airport and you can know that for sure.
All the problems in the video come from trying to use the letters to guess the areas they refer to. They might be related but they might also not. And that’s fine. Your booking site will let you type the full area name anyway.
The problem with metric paper is that A4 sucks for printing text—it’s too wide for a reasonable line length at 10 or 11pt, whence e.g. the sprawling margins of the standard LaTeX classes with the a4paper option; and A5 is definitely on the small side. (A single wide margin beside a long text column, like in the Berkeley physics course, Spivak’s Calculus, or Tufte’s books, is one possible way of taking advantage of wide paper, but it’s not used that often.) A period-2 infinite sequence with alternating 3:2 and 4:3 sheets, which in one form or another has been used for books since forever, would have been better, but apparently the committee(?) did not like it for some reason.
All the problems in the video come from trying to use the letters to guess the areas they refer to. They might be related but they might also not. And that’s fine. Your booking site will let you type the full area name anyway.