I've played it once, and my Mercenaries failed so miserably it was pretty much over by Turn 1
They made about 3 out of 8 involuntary surrender efforts, just hopeless.
I've had to play 4 times this scenario until the Mercenaries got a decent first turn. The it is worth playing the other three turns, and see who wins. It is a cat and mouse game.
If the first Mercenary turn just sucks, it is better to give up and start again. After all, it is a 'training' scenario.