Ajay, he has a couple options. One thing he can do is file a provisional patent for a few hundred bucks. Or, as you suggest, he can get people to sign an NDA. In reality, it takes so much time, money, and energy to get a product from idea to store shelf that the likelihood of someone stealing the idea is very low (lower than most people worry about). Market research is the #1 reason 97% of inventions fail, so worry first if the item will sell, and then second about protecting it. But that's my two cents.

Pardon the delayed response.