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.
We're a small company that wants to start sending a newsletter to our customers...but we can't do it without services like this.
Your service sounds too good to be true. I'm with Topica now and they're okay but I can't send my subscribers to a custom "thank you for subscribing" webpage once they subscribe.