Dude,
It depends a lot on what you want.

Carbon fiber epoxy composites have several advantages when used properly.
1. Weight savings. Prepreg Carbon epoxy is about 40% better strength to weight then aluminum. Sometimes this can translate into a significantly lighter part. You start running into wall thickness issues and buckling problems in some cases.
2. The carbon can be applied along any axis allowing the mast bend fore and aft vs side to side to be changed. It can be modified if it is not quite right in the first place. Ie start with is slightly soft and add uni carbon to get it exactly how you want it.
3. Carbon parts can be repaired with reasonable success.
4. It lends itself to home building techniques
5. It can be the difference between righting a boat unassisted and needing assistance.
6. Better reproducibility from part to part if quality control is high.
6. It looks cool.


Aluminum masts, etc are expensive initially because the cost to build a die is high. Mast blanks must be ordered in large groups to keep costs low. It costs a lot to change mast profiles ie buy a new die. There are definite quality control issues with aluminum masts, i.e. different weights etc. They need to be anodized.

Downside to carbon parts.
1. The cost of carbon parts can be much higher. Masts, etc are built in an autoclave and cured at high temp and 5-6 atmospheres of pressure
2. Material availability is a problem today
3. The failure mode of carbon is often catastrophic

Eric