RBJ,
If you do a search on you tube for the Necksgen Rev Test, you will see a video showing their own test's done at CAPE labs in Indy. Notice the head location and movement during the video. If you also search Hans Device Test you will see another test done at the Cape Labs during the IMIS show in Indy in Dec. 2012. Note the head movement in that video.

I will let you and others make a choice based on each of the test videos. However, I will say that ALL 38.1 Head and Neck restraints are rated for frontal and up to 45 deg angles. Anything beyond that is not covered by any of them. For REAL side protection you need a full containment head suround seat. This along with a 38.1 Head and Neck Restraint is your best option.