I received one recently for my birthday and installed it. I've never used a racing harness, so I cannot make a comparison, but the difference between standard and with the cg lock is like night and day. You can tighten the lap belt as tight as you want and it won't budge. The shoulder harness however, is unchanged as intended. For normal day to day driving it is unneeded, but for aggressive driving in the twisties it's great. A good value and easy installation as well.
I just got back from a ride through the twisties after installing a CG-Lock. The improvement in ability to handle the car is HUGE.
This US$40 device allows you to snug up the lap belt portion of your seat belt, and keeps it snug, so you are attached to the car much more firmly. It provides about 2/3 of what a racing harness adds in control, but is street-legal and convenient.
The ability to handle the car when you aren't fighting to stay in your seat is greatly improved, and hard braking can be much more precisely modulated, since you aren't being thrown forward during the braking.
IMHO, this is a bigger improvement in ability to control the car than my upgraded rear sway bar. It's a 2-minute install, and can easily be moved to a different car without leaving any evidence. Worth every penny it costs and then some - it's even SCCA-legal for autocross.