A carbon seat post is a BAD idea for a folder considering the extreme length. Think of "leverage" and you'll get the idea. It's a different story on a diamond frame such as a MTB or a road bike where the seat post will not be subjected to so much dynamic forces due to their short length as they would be on a folding bike.

Carbon parts are also known to fail catastrophically without any warning if they have been compromised by a gouge that you may not notice for instance. That's why experts most emphatically urge anyone who rides a bike with a carbon frame and or fork to inspect it closely before any ride.

Ed