Bidline has two failings:
1. If there is no movement in seniority, it can be a bit harsh on the juniors.
True.
2. It is complex, so a lot of people, especially those outside the company and new guys don't understand it.
Not really. Bidline Rules as a whole do take up an entire folder however, the work allocation system is totally transparent, so no-one can be stitched up and can be summed up in one phrase:
The more senior, the more choice.
Simply put, you bid for several lines of work. There is one line per pilot. The most senior pilot will get his (her) first choice. The second most senior will have to put in two choices to be guaranteed of one, the third most senior, three lines and so on. The fact that everyone bids for different things means satisfaction levels are very high. I remember getting my first choice once, despite being over two thirds of the way down a long list at the time.