A3 gives these letters to passengers whose flights were substantially delayed, irrespective of whose fault it was. There is a thread dealing with that, you'd have to search for it to see what kind of experiences people had. Very briefly, there are some "problems" associated to these trips such as extra seat availability needed, payment of taxes and twelve months validity. I'm not a snob but I never used two such "coupons", the first one because I had no free time to squeeze a private one way flight in my calendar and the second one because I simply... lost it somewhere on my desk (I know, I know, but it would have taken me a day of archeological excavations to find it
)