I never owned a carbon fiber neck bass but I did play one that I really liked several years ago. I opted for a much less expensive aluminum necked Kramer bass with a fretboard made out of a synthetic material similar to ebony or rosewood. The aluminum neck shared a lot of the same positives as the carbon fiber(great resonance, straight and true etc.).
What I don't know is, whether or not they share the same negatives. The negatives being that the wood of the body and the metallic material of the neck, expand and contract at different rates. This is a REAL big deal with aluminum. I don't know if it is or not with carbon fiber.
The Aluminum neck Kramer wasn't a real expensive bass, but it played great , sounded great, the neck felt great and was extremely strong. This is important to me because I play heavy strings(110 guage E) and have twisted a neck or two because of this. I thought this was the answer to my dreams, but it turned out to be a nightmare
When I played a cold room , that aluminum neck was like playing an icecicle. As the temperature went up I'd be out of tune, if the temperature went down I'd be out of tune. As the night progressed anything that influenced temperature or humidity would affect the tuning. It was weird the way it would tune itself upward as it would warm up. That thing drove me absolutely nuts
Once again, I never owned a carbon fiber neck and I don't know if it would act like aluminum, but this expansion/contraction thing is something to be aware of.
Rick