Talking about a previous company

I left my job at a small startup last month. I got an introduction to someone that startup is trying to hire from my network. This new contact wants to know what I think about the company before he makes a decision.

As part of my leaving the startup, I signed papers agreeing to not talk negatively about the company. How bad of an idea is to tell this new contact about my experiences? If I were to decide to talk with him, do you have any tips to minimize the chances of negative repercussions for me?