The Short Answer:
I had the opportunity to play one over a decade ago. I couldn't get over how heavy it was.
The sound had very little sustain and was for lack of an actual word to describe it - Thuddy.
The Long Answer:
Are you looking at purchasing a Fiberglass Bass, or are you interested in a Duke Bass from the original post which is manufactured using Carbon Fiber?
Fiberglass and Carbon Fiber are two very different materials.
Fiberglass is a favorite for boatbuilding due to its inherent flexible properties. Speed boats rely on this flexibility to cruise across choppy waves. This material doesn't translate well to create an instrument that requires rigidity to sustain the resonance of a sound.
While some companies had success using more compact fibers, most that made it to production sounded dead acoustically. If you were amplifying the instrument, it was less of an issue, however, they got a very bad rep due to the lack of acoustic sound quality. You can still find old Roth & Finch basses for around $600 on eBay. I believe there was even one in the classifieds here.
Carbon Fiber has given new life to fabricating composite instruments. In certain situations, it can be more desirable to have a carbon fiber instrument. Heat and cold have very little effect on playability and they are very durable.
Carbon Fiber can be manufactured to have metal-like qualities to the point of ringing like a bell, yet still be very lightweight. I recently heard from a well know symphony cello player that the main complaint about the Louis & Clark instruments is that they are simply too loud in an orchestra setting. Their projection overpowers the section.