EAC warns that just because a drive claims to be able to report C2 errors it doesn't mean it actually will, and offers that function to examine whether C2 reporting works or not.
I scratched a burned disc on purpose to use for this test and my drive did report a C2 error.
With all the suspicion raised on the feature, and the lack of a reassuring explicit confirmation, the question keeps bothering me: If the drive reports on one C2 error, does this mean I can fully trust the C2 detection and rely on it instead of the "Accurate Stream" feature, or is it still possible that the feature will only report some of the errors while others slip through?
The reliability probably depends on the drive model. However, even with drives that had a seemingly good implementation of C2/CU reporting (like the old Plextor drives like Plextor Premium which I had) can be problematic. Years later when I batch checked my library with CueTools Verify, I found some rips which were not accurate even though all were "securely" ripped either with PlexTools or EAC (with C2 error detection). So in retrospect I wouldn't really trust the C2 reporting, it is just one more thing that can go wrong ;)
@sTisTi Thanks for the input.
In the meanwhile I also landed here:
http://wiki.hydrogenaud.io/index.php?title=EAC_Drive_Options#Drive_is_capable_of_retrieving_C2_error_information
So, yes, it doesn't seem to be too realiable. Makes you wonder why they put it in at all. An error detection feature that doesn't reliably tell you about all errors that have occurred seems quite counterproductive to me, giving a false sense of security.