One of the funny things about this will be if you are sold Fast Track, the contract is strictly that you get to access the Fast Track lane.
I don't know if it is any more detailed than that, but it would seem that there is no guarantee that it will get you through security on average faster than a passenger who does not have access to the Fast Track lane. There's also no guarantee of the time it will take for you to get through security (though this latter one probably can't be helped so shouldn't be part of any contract).
I mean, if it were truly chockers, you might spend a long time in line, so to speak, but you should still complete security much faster than anyone who is queuing up without Fast Track. If it were the direct opposite, you might not have much of an advantage at all over the non-Fast Trackers, or you might actually be at a disadvantage.
If they use the same lane for those with disabilities as that for Fast Track, then the line might move considerably slowly such that much of the advantage of using Fast Track would be lost. Let's be clear - that's not any fault at all on anyone who has a disability who really requires more time to get through security, but they would probably do well to have a separate exclusive checkpoint to help such people so that other Fast Track passengers can progress rapidly.
I don't know how vigilant they are on the Fast Track thing, because the last time I went through, no one pulled me up. I forgot that QF status holders aren't entitled, and I don't think my Departures Express pass may have been effective, but it didn't matter because no one checked. If this were the case, you might think someone who bought Fast Track might be feeling a bit miffed.
In other words, you are literally gambling $20, and you will, under any circumstances, never see it again.
