For a prosthetic job, it looks good, but it doesn't quite capture the cherubic baby-face nature of Hitchcock's real face. What it looks like in motion will also be critical. Some of the old-age prostheses in J. Edgar, for example, may have looked good in still frames, but looked horribly stiff and rubbery when the actors moved around.
In the end, it won't be the make-up that makes or breaks the performance, anyway. Hopkins had barely any make-up at all when he made Nixon. His physical performance and mannerisms did an excellent job of capturing the man even though he didn't look much like him.