From the Johnny's Selected Seeds website:
"Benefits:
• Sows a wide range of crops with precision
• Virtually eliminates seed waste and the need for thinning, saving you money and labor
• Better germination rates as a result of improved seed-to-soil contact
• Accurate seeding in a variety of soil conditions
Features
• Interchangeable gears allow you to easily adjust seeding density in-row
• Transparent quick-release hopper (0.26 gallon) allows you to monitor seed level; includes a convenient sizing gauge for selecting the appropriate roller size; and makes it easy to change out rollers and seed in the field
• Standard shoe (included) is adjustable for proper depth control when seeding
• Handle can be adjusted for height and/or offset for footpath operation
• Foam-covered drive wheel provides good traction while rear press wheel covers the seed
• Includes a set of six sprockets for adjusting in-row spacing: #9, #10, #13, #14, and (2) #11."
Here's a video describing how to use the seeder: