Not too many people have one. They're down to 900 bucks which isnt bad I guess considering they're made out of my expensive material. I held one at the range and it felt real nice. The few people who have bought them say they work and go bang when needed.
The nice thing about it is it's blessed by the DOJ. The bad thing about it is the magwell is sealed pretty much permanently. So if you move to a free state, you would have a hard time converting it to a normal rifle. Some people say you can take a saw/dremel to the receiver and open the magwell.. sounds like a lot of hassle to me.
If you build your own off-list AR, you dont get that blessing and there is a chance you could get in trouble with it, even if it's built to the letter of the law. BUT, if you ever leave California, it can easily be converted to a normal AR-15.
If I were in the market for a CA, I'd get the Carbon-15. I dont plan on moving anytime soon.. and if I did move, I'm sure I could find someone to buy it. The major thing for me would be knowing it's completely and approved by the DOJ.