Not bad. If we give them an escape route, though, they might withdraw or run after the first few exchanges. We wouldn't wipe them out in one fell swoop that way, but we'd take less casualties and hopefully still force them to be herded and at a disadvantage.
The disadvantage to the herding tactic, though, is that they know the land better than us, so they could (with some good rolls from their commander) lure us into some crappy terrain where they gain the advantage, or sucker us to a place where another Frankish force could be close by.
That being said, I'm leaning toward smashing them here and now so we won't have to worry about them later on.