I understand the final physics are quite different to the demo. The arcade (or 'simulation' physics are quite fun, but a lot less difficult than pro-sim - you don't get horribly spanked for your mistakes, but can still lose time with wheel spin, locked wheels and the like. Imagine the original PSX Toca games, without the sudden breakaway.
That's through the wheel setting, anyway - I have heard the 'gamepad' setting is much more forgiving, particularly on throttle and braking inputs.
On 'simulation' (as opposed to 'pro-sim' mode) it is still possible to get yourself into fairly serious trouble, particularly in the more powerful cars.
It's still 1000% better than TOCA Race Driver - the cars actually feel connected to the steering, so it's much better to drive. The Formula Fords in particular are a hoot to drive, both in-game and on-line.