Comfort is a critical factor in the design of a restraint. If a driver isn't comfortable wearing it, he likely won't wear it correctly-or at all. Ashline uses a foam pad that sticks to the seat and keeps the "backbone" of the device from digging into the driver's back. Because it sits into the pad's cutout, it also helps hold the driver in position.
If you have the opportunity before purchasing, Ashline recommends the "10 minute test." With the restraint and your helmet on, and your belts strapped down tight, simply sit in your car for 10 minutes as Hargett is doing here. This will give you a good idea whether or not the device will hinder you from concentrating on driving your car during a race.
The SFI-38.1 certification is the most stringent standard today for head-and-neck restraints. If you are serious about protecting yourself, you should make sure any restraint you purchase meets these specifications. You will know whether a restraint is 38.1 compliant because if it is it will have a sticker like this somewhere on it.
If you have the opportunity, make sure to try getting into and out of your racecar with your restraint on. If it keeps you from getting out quickly when there is a fire, the device isn't very safe after all.