5D Mark III In-Camera vignetting control

Hi,

I am about to buy a 5D MK3 with it's kit lens (24-105). I know it has in-camera correction for vignetting (light fall-off if you prefer) as long as the lens data is loaded onto the camera (in this case it would be).

What I am trying to figure out is how good this feature is or how well it works. If I am using the 24-105 at F4 24mm, there can be some light fall-off depending on the exposure. Would the camera get rid of it completely or partially only. Any experience with that?

Correct me if I am wrong but my understanding is that since it relies on lens data for the correction, then it only corrects light fall-off and not actual vignetting from let's say a lens hood or filter? Am I right?

I'll try this in a different forum too to see if I am lucky.

THanks a lot.