But not necessarily "useful", though. In Maradon he had to fight, and make gateways. It may be at Maradon, when the real fighting against the Shadow started, he decided to use his secret angreal even if somen other Asha'man might notice he has it.

Of course, the "nobody knew he had it" may be contextual too. If he's at the BT/about to try infiltrating it with a MOM, he may actually have everyone at the BT in mind when he reflects "nobody knew he had it".

But it could also be the POV of a dreadlord who was at Maradon. And many other things. It could be another Asha'man altogether who's grabbed it. It just seems like everything revolves around Naeff nowadays! RJ would more likely have used Flinn or Narishma, but Brandon seems to involve Naeff in everything now. Naeff works with Bashere's soldiers, Naeff puts out the fire at the manor, Naeff goes to the Seancham, Naeff rides with Rand through Ebou Dar, Naeff goes see the Borderlanders, Naeff becomes Nynaeve's handy Asha'man, Naeff gets healed from the taint, Naeff goes to Maradon, Naeff gets sent to the BT. Rand's in love or something (might actually be Brandon who is...). Narishma must be murderously jealous - he used to be the Asha'man Rand trusted with that sort of things.

I just really doubt it's a Rand POV somehow. Why would a medium angreal be so important to hide when he carries Callandor on his back?

Of course it may not refer to the little fat man either, though it seems likely somehow.