I think the real risk for this is when you try to change regional flights. Less room for error so to speak, especially with less frequency than its main trunk siblings. I tried to use it when flying TRG - WSZ (back in the day). I had already prebooked my WLG-WSZ flight through Grabaseat which departed at 4pm or something. There were 3 flights out of Tauranga which arrived into WLG before the departure of the flight to WSZ. There was a flight departing TRG at 7.00am for $189, the other two were over $300. I decided to chance it and book a flexitime fare on the 7 am one, and try and change. However despite getting up at midnight to execute the change, all flights were full. I ended up with a 8 hour wait at WLG. Lesson learnt on that one..
