It appeared to me more like a (poorly depicted) version of what Asmodean did for Rand after he overstrained his channeling during the battle of Cairhien - pushing some raw Saidin (so in this case Saidar) back into the channeller to prevent burnout (in this case fatal burnout rather than losing the ability to channel). So not an unprecedented action.

My point is that letting Nyn read it when Elayne is right there is not a relevant point as Elayne had no particular ability in the books to know what a ter'Angreal does - only an interest (and perhaps a talent) in learning how to make ter'anreal - it was Aviendha who found she had the talent to know what an existing ter'angreal does (and much later). Nyn got the sense of suffering when touching the male adam, in general if a male who can channel touches an active adam he and those wearing it suffer great pain, if the bracelet is put on a male who can channel while a woman who can channel is wearing the collar then both die from it. The male adam was designed to allow one or two females who can channel to control a male who can channel, there is no general adverse effect from females touching it, only Nyn got the impression of suffering.

Nyn was the one who got impressions from objects in the books (e.g. the male adam equivalent in Tanchio), although Aviendha was able to read the purpose of the ter'angreal from the Ebou Dar horde.

In the books they are no more threatening than the Saxville-Baggins' in LOTR. In the show they have added heavy drinking, womanising, gambling and an implication of Mat acting as a thief or gigolo (depending on your interpretation of how he got the jewelry he sells to Padan Fain). Overall a far more gritty two rivers compared to the shire-ish view in the books.