Ahh, that famous Freudian penis... slip, slip, I mean Freudian slip.
On that topic, Freud has nothing at all to do with mentalism. I suppose the tentative link would be that Freud was the first psychologist- well, the first psychologist as we know psychology today, really- to argue that everything we do is influenced by the 'complexes' in our minds. In his introductory lectures on psychoanalysis, he told a story of how he asked someone to think of any name his client thought 'Albina'. Freud argued this was because there was a joke running between him and his client that Freud always called him 'Albino' because he had really pale skin. When he repeated the experiment the other person thought of someone who they were falling in love with, but hadn't yet realised this was so.
Reading through passages like this of Freud, one immediatley is reminded of Milton Erickson and his philosophies on the unconscious which is much more 'mentalism' related.
Also, Paul Ekman, a favourite name to drop by mentalists, when he was younger was an expert on Freud, he claims he has since forgotten all he knew, but that he used to be able to quote Freud on any topic given to him and that others must have found him very irritating for doing so!

Similarly when one thinks of Ekman's work, which was heterodox namley because it was beleived 'there is nothing significant in the face' and Ekman, arguably influenced by the neo-Freudian school of thought, saw significance and unconscious processes in virtually all actions. Perhaps this is why Ekman said in an interview that if he could start his career again, he would study handwriting given that most interpretations of it are overlooked as pseudo-science.
On the topic of the Oedipus complex, it is important to remember that Freud argued these ideas would have succumed to 'infantile amnesia' as he would say, or they would have been 'repressed'- ie, you won't remember these feelings because you were a child and because your mind doesn't want you to remember. Nonetheless, you are still correct. The Oedipus complex is nonsense.
Studying psychology however, will teach you very little about human beings. If you read about quantum mechanics or the even more delusional pop science books written about it, then you will be told that observing a system disturbs it such that your observations are no longer valid. Obviously physicists have never tried to understand human beings. The more humans believe they are being watched, the stranger and stranger they become- this is more than a quantum system being disturbed, this is a human psyche! The best way to understand people is to ask 'why?' for every action, however small, someone does. Or to ask 'why and how' someone is the way they are- paying attention, not neccesserily to detail, just paying attention is rare enough.
Asking simple questions, although they seem obvious, are- as it happens- rarley asked, thought about or observed and they will take you a long way. And since we spend our lives surrounded by constant psychology experiments and have the whole of history to look to for social experiments, we can virtually do away with statistical research and analysis and replace it with our own daily, intimate observations, which are much more valid if we pay enough attention.
But anyway, by now I have had to restrain myself from an attack on the epistemology of many social and quantum 'sciences' and I could talk forever and still say nothing relevant, so I think I shall stop here.
Oh yes, and despite my brief digression about psychology since you started me off on Freud and its relation to mentalism- psychology still has nothing to do with mentalism. Nothing Derren does uses any unique psychological prowess whatsoever. At all. Ever. Well... sometimes he uses something very simple. But nothing, nothing at all like what you think. At all. Ever. Ok, I'll shut up.

''To go wrong in one's own way is better than to go right in another's.'' Dostoevsky's Razumihin.