The flex heads follow the ground using springs. If you have tilt on combine you don't use it. You need someone that knows how to set them up. There are a couple in our county being used and it seems like they are constantly adjusting and working on the head.
The MacDon does have built in tilt. As far as Jeff's comments go, you do have more adjustments available. Other platforms have no adjustment capabilities. It's been my experience once your Macdon is adjusted for your combine, its good to go.