A finished VN? Now that's a rare sight.
As for the secret end.....
What was the point of the experiment? Dave remembers everything, so that must mean the lethal medicine Oswin created is going to work or something? Paths A and B both had pretty good endings, but path P is just "what if we went to the beach instead?". Sure, it's the best trauma free timeline (assuming the brain damage from memory overload won't be a problem), but I don't see it working at all with the rest of the story.