I'm doing this one again.
Story Origins is like BookFunnel--you offer a free short story, novella, novel and in exchange receive an email address. Unlike BookFunnel, StoryOrigins is currently free.
During my last release, I compared sales from my organic list to sales from my Story Origins / BookFunnel list. The book was full priced and wide. I found that StoryOrigins / BookFunnel subscribers DID buy, however it was about half the rate as organic subscribers.
Still, since it's free to join StoryOrigins, and free to participate, you have nothing to lose. Also, you can build your list much faster with StoryOrigins giveaway. In the end I sold as many full-priced books to my StoryOrigins / BookFunnel subs as I did to organic subs just because of sheer volume.