The Book Crawler database can be transferred to another device through the backup/restore mechanism.
The fastest way is to use a single Dropbox account to perform the transfer. On the device that you want to copy, press Settings -> Import/Export. Now, press "Link". Press "Backup" to copy the database to the server. From your secondary device (the device you want the database transferred to) go to Settings -> Import/Export. Link to the same account as you did before. Press "Restore" to replace the database with the one on the server.
IMPORTANT: To merge results with another device, transfer the CSV file. The CSV file is all text, so it won't be able to transfer images. To do this, go to Settings -> "Update Entries" to download missing artwork from the internet. Only transfer the database if you want to replace the database.
You may also email your database under Settings -> Import/Export and press the "Email" button. If your database file is small enough, it will attach the file directly to the email. If it is not, it will provide you with an option to upload the file to dropbox and attach a share link into your email. You can control the maximum size to allow for attachments under Settings -> Max Attachment Size.
It is also possible to transfer your database file between devices by using iTunes file sharing.