I have a Tembo and a Redman, both finished from blanks and both with the carbon strip. I personally believe the carbon strip is worth the extra, but only if placed directly under the back glass. I request black glass for the backing for that reason.
My Redman seems a bit smoother, but the Tembo is a bit faster, although the Tembo is 55# and the Redman is 52#, so that no doubt accounts for a few feet per second extra speed shooting the same arrows.
I had a Halfbreed that had the carbon under a lam of yew on the back with clear glass and it did not seem to add much zip.
If I were to order a Halfbreed today it would be with a lam of yew under clear glass on the belly, 2 lams of carmelized boo and a lam of yew under black glass and the carbon strip next to the black glass backing. If I was going with a heavier draw weight, say over 60#, I would perhaps opt for an extra lam of boo, but my Tembo has just 3 lams plus the carbon and it is as good as it gets at 55#, in my opinion.