An inventor with a nonpatented product must walk a very fine line. If your paranoia is too severe, your stringent attempts to safeguard your idea will turn off other parties. But if you're not careful enough, you could lose the rights to your own idea.
Don't be penny wise and pound foolish when it comes to NDAs. Hire an attorney to write them for you. If you think that's too expensive, write the NDAs yourself and have your attorney edit them. But remember, your idea could be your future. Invest in it wisely.