I've have the original Griffin iTrip Auto and we really only use it on long journeys.
I'm generally quite happy with it.
Only a few minor niggles:
1, Interference on busy roads from other cars with FM transmitters on same frequency. This new model might have addressed this.
2. It has no internal battery, so it switches off when engine not running. It may depend on your car if the cigarette lighter works when engine switched off.
3 It doesn't charge our 4G nano. Again, this is probably addressed with this new model.
4. Get a bit of interference when passing under or near electricity lines. Can be annoying if lines run alongside road for a distance.