The fact of the matter is that there is only one 5th Generation jet available to western countries. The advantages 5th Generation jets have over 4th (and 4.5) Generation jets are published. If you don't get on board, in ten years you will lose.
The over-runs/issues/flaws? That's the rort factor coming into play. This is Capitalism.
They will sort it all out, eventually. It'll be at a rediculous cost, but it'll get done.