An often talked about option for marketing books (especially fiction books) is eBook discovery services like Bookbub, where readers sign up to regular e-mails of discounted books and authors pay to have their books listed. But how good value are these services? What do you need to get listed with one? Which are the best for which genres? I talk today to Alli’s watchdog John Doppler who has done a comparison of these services about what he found out.