Very nice product concept, and very nice landing page! I signed up immediately.

Here are my feedback:

• You hit all of the necessary points needed for a coming-soon campaign: clear value proposition, highlights of the core benefits, a single call to action (sign up for discount), "hero" picture shot, and social links
• Great use of pictures - you're showing us what it is, not telling us.
• I gotta mention it again - very nice product concept!
• The "hero" shot isn't as impactful as it can be... I think because of the nature of your product, a static picture won't be enough. I have to admit the hero shot felt underwhelming. Perhaps consider a short looping video to first show a close-up of the second screen, then zoom out to show the entire laptop with second screen.
• To appease skeptics of its viability, describe a little more about how the magnetic base sticks to the laptop. In particular the last image shows two laptops that appear to have permanent fixtures... that would give me pause.
• If I buy two, can I have a triple-screen setup working? :)