Bob:
Here is
a recent thread on this.
No conclusion really. Didn't run HANS at VIR SVRA finale as planned.
Chris: HANS only works if you have the shoulder belts to hold the collar down. Thus, need 5-6 point harness. You can use with stock seats as several on this board do with a harness setup. For price info just got new belts in tub from mrpoducts.com. Cam-lock, 3", 5-point setup for $68 each. Total $136. These do NOT have an "H" that holds shoulder straps together (behind stock or track seats). Don't need if you have a crossbar in your roll-bar.
IMO the "ultralite HANS device" (CF) for ONLY a few hundred $ more is not worth getting.
Jase