The CG Lock is a wonderful inexpensive seat belt upgrade that is easy to install in just a few minutes and will definitely keep you planted in your seat for either spirited twisted mountain roads or for a day at the track.
As you may have noted, even though the Z8 seats are comfortable, they really are not designed for hard cornering. The side bolsters are adequae but the seat itself really lacks any side support necessary for hard cornering, especially if you are at the track. Their claims to be similar to a 5 point harness I am not sure about but I can tell you this thing does work.
I found this CG Lock, available at Bavarian Auto or directly from CG Lock, for $41.96 plus shipping. It installed in just a few minutes and most definitely made an improvement in keeping me firmly planted in the seat at our recent Texas Motorsport Ranch outing in October.
I would recommend it highly to any one who either does spirirted driviing or who goes to the track regularly.