I think both Corksport and Cobb's try to trick the ECU. I've seen a couple posts about a CEL coming and going with the Corksport but I don't think theres been any serious problems...or it might have been a problem when it first came out and now it's fixed? I'm not sure. I read the Cobb AP will be able to disable that CEL or something if you did have that problem.
What do you mean by does it have to be flashed?
What do you mean by does it have to be flashed?