I've held them and can't say I was impressed. Like Benhs said, the nimbus was pretty awful. The tail is a solid piece of resin and the silver ring was cheap metal. Also, the kickstand was poorly assembled, held together with ugly screws instead of welded or otherwise fixed. The tail is also attached to the handle with a rather hideous screw that is very exposed. The Handle felt hollow and did not impress me.
As far as the Firebolt goes, the handle is slightly better (but still very obviously plastic) and the tail is a little better. However, where the end of the tail is individual pieces of plastic, the part where they meet the rings is again a cast piece of resin. In my opinion, it is not an effective piece. I saw the real props in the Seattle museum exhibit, and was very impressed with them. Aiming to take what I saw there and create my own replicas. I've done the Nimbus 2001 before, using fiberglassed rope for the tail and a carved/sanded wood handle. Made the kickstand out of steel and wire brushed it to give it a nice polished look.
Anywho, in summary, if you have the skills, you can make a better broom for less than what the Noble Collection is going to charge you.
Good luck man!
i