These are crash test videos at 42 mph
Harness without HANS
Lesson: If you like your head attached to your spine, always wear a HANS device when strapped in a harness, whether your driving or riding along. If you're not willing to do that, save your family & friends the trouble and stay with the stock 3-pt belts. Stock belts + airbags do an excellent job of protecting the occupants.
Derailing my own thread: On the topic of airbags, there is no hard data I've found which suggests to either disable or enable airbags when combined with harness & HANS. My personal preference is to leave airbags disabled when using harness & HANS simply because the two systems were not designed to work together.