The seat post clamp that came with my frame was poorly finished, and the curvature didn't match the seat post. As a result, the sides have dug into the carbon post and cracked it after only a few hours on the bike. As you can see in the image, there's a big gap between post and wedge.
I've messaged TanTan, but haven't received a reply yet. I've sanded it down to match the diameter, hopefully it works now; the seat post has to be replaced though.