I can't be assed to check if anyone has answered this already, but by the core book, getting the same talent twice in the origin path grants you the Talented (Any skill) talent, which is quite handy to have for Dodge and such.

As for being detected as a psyker, any other psyker with the Divination discipline can tell you're a psyker with a simple psyniscience check, using the Aura Reading technique. You're boned.

Regarding Talents:

The Into The Storm supplement provides an alternate rule where you may choose to get 50xp back if a skill / talent is duplicated (As the origin paths in that book cost XP you are effectively getting a discount.)

Regarding Psykers:

Yeah that was one of the powers I asked about in the previous page along with the Navigator's "Gaze into the Abyss" power? "Gaze into the Abyss" is an opposed roll at least but the Aura reading is not even that and I am assuming there are other techniques similar to these two that I don't know about.

Is there any technique by which one may hide their psyker ability? and/or force an opposed roll on things like aura reading?

Translate 'drop of a hat' to 'a momentary lapse at the wrong moment after a lifetime of constant worry and anguish that your dreaded secret will be discovered', then?

This is what we were hoping for actually.

The guy who wants to play the Rogue Psyker is fairy ok with the consequences of being discovered especially if he does something stupid (although he might take steps if it was just one or two random people who have not been able to pass on the news) but none of us want him to be discovered just walking down the street or a genuine by chance meeting with an Inquistor at the governor's party.

TBH, the biggest threats are when entering a civilised Imperial system (or entering an area secured by someone psyker-savvy who is not afraid of their use). I imagine (and have had sort-of confirmed in Kill Team [Gav Thorpe]) that the majority of starports in Imperial space have a sanctioned psyker working in Customs/Immigration to pick up rogue psykers trying to sneak about. Of course, simply as a matter of logistics, there can't be such a detail at every starport on every planet- the large interstellar passenger hubs, yes.

Naval yards, yes (although in theory every crewman aboard vessels of His Divine Majesty's Imperial Navy should have been screened as part of the enlistment/impressment process [see Relentless ]).

Random orbital cargo transshipment dock no. 237? Not so much (likewise the purely local interplanetary spaceports will have less security).

Private landing facilities for the rich, politically well connected? Really shouldn't be a problem, in practical terms; sure, in theory, you should be dealing with Customs and Immigration or some other TSA type process, but as a member of a Rogue Trader's retinue, all it takes is some bluster about not trusting psykers at all, (limited) diplomatic immunity and orbital bombardment and you should be golden...

As for hiding one's powers- yes, in fluff there is a technique that can hide or suppress psychic ability from a casual scan (although Mind Scan could well pierce through it if they went deep enough). I'm not sure if it has had rules worked up for it though.

In a similar vein- the null rod, or equivalent psychic warding/shielding device may well mask a psyker's powers, but at the cost of suppressing them at the same time (there are also injectable psy-blockers which would do the same thing, albeit without an easy way to get rid of the suppression in a hurry- you'd have to wait until they wore off...)

Is there any technique by which one may hide their psyker ability? and/or force an opposed roll on things like aura reading?

In Deathwatch, yes. In Black Crusade/Only War I'm not sure. In Rogue Trader I'm not familiar with any and I have looked into it. I came up with the Null Rod idea as a house rule workaround that made sense to me, but otherwise no.