I just finished a build with a Proof barrel - a 28" Sendero contour on a 28 Nosler. It is my first CF barrel, so my sample size is very small, but here are my initial impressions (up until now I have only ever used Bartlein and Krieger).
Cosmetically: The Proof is downright gorgeous. I am with you on carbon fiber; it just has a unique and awesome look, and the Proof is particularly well executed in this regard.
Accuracy: The Proof seems to be comparable to my Bartleins and Kriegers chambered by the same smith. Half MOA consistently, showing signs of even better. Only a sample size of one barrel though. I have had 10+ Bartleins/Kriegers all shoot lights out, so I am more confident when describing the accuracy of those barrels based on consistent, repeated performance.
Weight: It is not as light as you might think. It is definitely lighter than a steel barrel of the same contour, but the weight savings are not game changing to me. I saved about half a pound over a light palma steel barrel.
Finish: The biggest difference I have noticed between the Proof and my Bartleins/Kriegers was the level of carbon fouling. I don't know if that is attributable to the level of finish lapping, but I can say that all else being equal (powder, primer, projectile), the Proof fouls more and faster than my other barrels. Since mine is a hunting rifle that will never see extended strings, this isn't a big problem for me. The Proof also took way longer to break in than my other barrels (by break in, I mean the point at which copper fouling becomes negligible). I have seen Bartleins stop copper fouling in as few as three shots. I was still running multiple KG12 patches to clean copper out of the Proof at 60 rounds.
Price: Come on. We are talking about carbon fiber. You know what you are getting into.
All in all, I am happy with the Proof. It makes for an especially gorgeous rifle when paired with a carbon fiber Manners EH-1. For high volume target rifles, I will probably stick to steel barrels with cost being a main driver.