Solo direct mail is more effective than coupon books for a few reasons. First, solo direct mail reaches a more targeted audience. Instead of mailing a coupon book to a wide range of people, a solo direct mail campaign can be tailored to reach the right people at the right time. Second, solo direct mail offers greater flexibility. You can design your own mailer that lets you highlight the features and benefits of your product or service. You can also include offers that are customized to individual recipients, allowing you to make the most of each contact. Finally, solo direct mail is often more cost-effective than coupon books. By targeting the right people with the right message, you can get better results with fewer mailings.