In terms of construction, there is bugger all difference, and only a few hundred grams weight difference from the carbon to the fibreglass hex core "entry" level harness.
Have only use my carbon spreader version with a rope and a ring to attach my C-Loop, I had one of the first in Oz, still going strong, original rope, and I kite almost every day its windy. I don't jump much on my surfboards but when I do I have no issues with the harness at all I was using a dynabar for years prior so I'm very used to hooked in jumping with a sliding spreader arrangement.
I'm a size 33/34 waist and this is the size L carbon elite thing.
A guy on the beach asked me about it yesterday he was super interested, wanted to know if I though it was worth it? I just said the answer is relative to a persons circumstance, but just in terms of function, comfort and durability, worth every cent for me.
Here are some pics to show how it is wearing