I have a defnder. I really like mine, plus the price is a plus. Its a bit of a pain to get the belts exactly where they are supposed to be by yourself in the car though. That is the only thing that I can say I don't like about it.
The thing I really like about it is it has tethers to limit your side to side head movement. If you look at the pictures, you can see them off of the black stabilizer bar, they're maybe an inch or so long and tie into the bottom of the hardware that attaches to the helmet. I feel this is a great and important feature for the guys that don't have a containment seat, because it protects if you get hit in the door. I believe the HANS is intended to be used in conjunction with at least a halo for that reason.
Justin