I think this is an excellent way to acquire paying customers AND will give many potential users the option to see if they can build a decent subscribership without having to front the $250 or more that would be needed for ListBuilder.
I am impressed with the simplicity of your product.
I've seen a handful of online list managers with a ton of powerful tools, but this is easily one of the simplest I've seen. Don't be fooled by its ease of use. [Ezine Director] packs a powerful punch. Give it a spin!