For my large model of a clock I wanted to use a 3D tracking marker because what i learnt from earlier project where if the user wanted to explore the model you would loose tracking from the 2D image, so to get over it I used a 3D tracking marker so that when you looked at it on a level plane it would still track. These would be ideal of an in store kiosk using foam cubes and tracking multiple models to it so it can be picked up and rotated.
Dan's Blog 