Do you have investors? Check any documents or shareholders agreements you've signed to make sure you can actually do this type of work without breaking an existing contract. At the very least you may need written permission from your investors in order to go ahead.

As for signing an NDA, I've found that often people who require them are pedantic about unimportant things and difficult to work with, so unless there is a very good reason they'd need one I'd be very cautious about getting involved.