My thoughts: I did extensive research into a perceived "weakness" in the carbon fiber. AP had all-carbon cases/bezels before they designed this one (Alinghi, etc.) and they put the ceramic bezel on the 26400AU.OO.A002CA.01 to prevent the "chipping" that may happen in carbon fiber. So, the reality is, on the case of this watch, I suppose you run the risk of it "chipping", but it is very uncommon and since the case is not really exposed like the bezel (which is ceramic) and I am not very rough on my watches, it was fine for me. I also believe that some cases are more susceptible to this "flaking" than others, so if the one you are looking at is perfect, it may not really be an issue at all since the watch left the factory more than six years ago. For what it is worth, it is possible to get a new case for this watch for about USD$2,000 if you wanted to go that route.
As far as the edges not being "sharp" -- that is the way they came new because there are limits to what can be done with the carbon fiber. The case on a pre-owned piece should be examined carefully to see if it has been "chipped" or "flaked" in any way -- don't buy it if it has been. As far as wearability, I love mine. It is very light and the size feels smaller because of the black colorway. For an AP Royal Oak Offshore, this watch is about as "stealthy" as they come, yet still stunning, and I like that.