I tried heaps of composites stringers , carbon and other materials in the mid 90s
the carbon was super light but did not like being loaded beyond certain limits when put on edge as per a normal timber
the rebound was awesome but I eventually broke all of them and 2 on one indo trip

I found also laying the carbon as a stiffener under the deck laminate and rails as per our current construction also has faster rebound properties with reduced risk of breakages.
hey mick check out the alloy joy I bet you its twisted ? I also tried this stringer and found under huge loads the aluminium didn't retain its shape