Ask HN: best practices for Launchrock or other landing page solutions?

I'm about to start preselling a B2B solution, an MVP, lean startup style. We already work in the industry and have a decent mailing list of brands that we can write to. I also want to put up a landing page, where I can start gathering e-mail addresses. The question is whether Launchrock is the best solution for this kind of lead generation. Does anyone have any experiences that you can share about the process of using Launchrock of similar solutions (like Lander)? Any lessons learned that are important? Thank you for any help.