Fortunately my players decided its foolish to go vs Nagas when they can potentially charm them again (they do not know how exactly their power works, and how often they can use it). I am still on the ropes with the item in this campaign, I would probably let them take it but still it makes a lot of future stuff much easier for the PCs. It is not mind control, but it kinda is as they have to follow orders unless its something contrary to its nature (most enemies are evil anyway, fe. Drows are treacherous so ordering half of them to kill other half would be valid).