I would really appreciate feedback like this. Especially if it focuses on specific things good or bad, like a lighting artifact, hair, hurried postwork, or whatever. If anything, knowing that someone would actually say something about the flubs, I'd probably spend the extra time needed to fix the stuff that I know is wrong before uploading it. In general though, I think you should only comment like this if the person asks for it or you know that they are open to it.