Here is a little clip to illustrate, comparing my friend's Audi S4 through a left/right complex. Obviously, I realize there is a performance mismatch compared to the 12C, but if you watch closely, you can see Brake Steer working and the S4 footage serves to amplify the difference.
The S4 is the first part of the clip. The left-hander is a compromised corner, since you need to get back to the left quickly for the next corner's entry. He has a little understeer, but recovers well to get set up for the right hander. But then, he tries to carry too much of that momentum and understeers badly in the right hander, which is actually a tighter corner than it looks on video.
Next, my 12C. I'm through the left-hander cleanly, with probably a little bit of assist from Brake Steer, helping me keep the car from tracking all the way out. But then, watch closely on the entry to the right-hander: At turn-in, for a split second the car understeers, just like the S4 did - you can actually see the car wanting to push left to the outside. Then, the next instant, the nose darts back to the right, towards the apex. (don't look at the front of the car, instead focus on the apex and you will see it easier)
By my stopwatch, that's about 2.5 to 3 tenths of a second gained in that left/right alone, which is mostly braking and turning, but the bigger gain would be at the end of the next straight, the 12C having been able to get back to throttle sooner.
I think what some journalists are doing, when they feel that initial split second of understeer, is taking off some lock to kill the understeer, from instinct. Which is exactly what you don't want to do, because that will also tell Brake Steer it's not needed any more and then you are in no man's land, sailing wide. You actually want to keep steering directly to the apex and get back on the throttle as quickly as possible, which will keep Brake Steer working, without interruption, through the middle phase and exit phase of the corner. The tricky part is that you need to trust that Brake Steer will kick in.