Well, we actually made it because we wanted to use KissInsights on our other startup SocialBlaze, but it was too expensive (we're bootstrapped). So we made our own for ourselves and decided to open it up and charge a price we would have paid instead of making it.

Honestly, right now it's just price (and even free surveys are customizable) and the fact that you can setup a follow up action such as asking for an email, asking to follow you on twitter, or like you on facebook. So if the user is already engaged enough to answer the question, he/she is more likely to give you their email or follow you on twitter/facebook. But we have a few other ideas on what to add to make this even more useful and differentiate ourselves better.