SoRCon 11 23-25 Feb 2018 Basildon UK http://www.sorcon.co.uk
I think a good contract is all I really need, but NDA’s have the added benefit of a man’s word being his bond. Breaking the NDA is less likely.
I've done some things for at least one professional, including being in possession of some actually sensitive information. And the subject of an NDA has never come up (except from one publisher who failed to understand the situation and rapidly dropped it).
But I would sign an NDA under the right circumstances. First among which is that you are paying me. And not a nominal sum.