Anyone knows what are they used for?
Do they provide a bonus to rolls, help with anything? Or are they just symbols of their status as sanctioned psykers?

Have I missed anything from the book?

Status symbol, helps to keep the withered crones upright while they recite the latest news from Scintilla. You might also see them used as psy-focuses, but those would be beyond the standard rank and file.

I would expect it to count as a psy-focus - most staffs associated with the adeptus astra telepathica seems to be psy-focuses by default, but in the end, it's something you'd have to argue with your GM.<br /><br />Other than that, it's just a regular staff with the shapes and markings of the Adeptus Astra Telepathica on it, identifying you as an Astropath (along with your robes and lack of eyes).

I would expect it to count as a psy-focus - most staffs associated with the adeptus astra telepathica seems to be psy-focuses by default, but in the end, it's something you'd have to argue with your GM.<br /><br />Other than that, it's just a regular staff with the shapes and markings of the Adeptus Astra Telepathica on it, identifying you as an Astropath (along with your robes and lack of eyes).

One would think that the latter would be the dead giveaway, but the people of 41st Millennium can be really thick sometimes