I often talk to potential venture investors, fellow developers, friends for networking and get feedback about my startup, ideas, features etc. In most cases the response I get is a blanket "ya, that makes sense", but at times I get asked some tough questions. These questions are not usually around technology, but mostly around market fit, differentiating features etc. These questions are extremely important so I can rethink and fine tune my approach and identify potential holes that I did not think about.
During these conversations I even talk about my future plans, product roadmap, market fit etc. I never asked for any NDAs or any kind of agreements from any of these investors(not that they would sign even if I ask) because I don't see any need for such agreements.
In my opinion, not talking about an idea for the fear that someone might just copy it is just absurd. Any idea especially a software product, even if someone thinks that it is novel and unique, is most likely not at all unique and novel. A lot of people would already have thought about it and if no such product already exists, it wouldn't exist for a reason. If you are secretive and do not want to talk to others about the idea, you will never hear about other perspectives and end up wasting a lot of time working on that "novel" idea.
When it comes to startups, ideas are cheap. It's just the execution that matters. There are a lot of factors that comes into play for a startup to be successful, it's never just the idea. Even if the idea has value, the initial idea usually goes through metamorphosis many times by the time the final successful product is built.
Talk to as many customers, investors, friends as you can about your ideas, only then you will think about your idea from a different perspective.