I have the top gun single chrono and here is what I think of it....
Firstly, the chronograph mechanism is a bit coarse however the reliability of 7750 is well known. Overall the accuracy of this piece is unbeatable.
Secondly, the ceramic case is fantastic in black. It comes with sort of natural black hence it gives a true impression of being steatlhy. However due to over-confident on the hardness of the case, I tend to take care of it less while wearing and that posed a problem. I have accidently hit the sharp end of a glass table while having a conversation and granted that the watch was "almost" invincible as there was not a scratch. However at close inspection, I saw a very very tiny bit of the case was chipped and believe me, that hurt like hell (after 1 week of wrist time only). Later, I found that there is no way to repair it and I have to live with it for the rest of the watch's life.
The top gun is trully a beautiful piece... You will love it whether its the single or the double chrono. I find that the main downside of this piece is that its not a limited edition hence you can get it whenever you want. All I am saying is that if you believe in IWC, then this is not a timepiece to be missed....