Generally, requiring an NDA before even talking about the product you would presumably be building; seems like an amateur move. It would make perfect sense for one to be part of your employment agreement though.

If the people you're talking to can't distinguish between talking in general terms about what you would need to be doing to be an effective team member. And talking about the specific details of the product they are building; which they have a right and responsibility to protect. You might want to reconsider working with them.