[kzhahou]

> In a meeting with the investor they have informed us of a market opportunity, a specific niche, where our product could be adapted

So what? Anyone can come up with ideas of market opportunity.

> there's many things about the investor that make it an undesirable partner (some parts are good, but most are bad)

As others have said on this thread: trust your gut! It's simple, really.

> We are afraid that this NDA could be wrongly leveraged in the future, if we end up pursuing and reaching this market.

Exactly, because you already don't trust this investor. Your gut tells you they are wrong for your idea, and your gut is telling you they'll hurt you in the long run.

I think what's really going on is this "investor" doesn't really have solid leads (maybe just some emails, maybe just some casual contacts at some companies). They will bring no value to your idea. As they have no value, they go for old-fashioned contracts to attach themselves to whatever newbie entrepreneur will trust them.

Good luck! :-)