Waitlister has all the features I need and it is easy to use. It also includes additional features such as CAPTCHA, confirmation and forms. Honestly, unless you are a little paranoic, why would you complicate life to your early adopter? Bring home her email ASAP before she changes her mind.

Despite being apparently simple, the application is well engineered and documented. Should I consider an "in-house" solution, it would cost me much more before writing the first line of code. Whatever other alternative would cost more, require deployment and hosting.

So I am really satisfied with the solution. I can now check a product idea by sharing some information and mentioning the waitlist. After that, I will do interviews and start development if I get a good interest.