While the app has a mechanism for taking periodic automated backups that allow you to restore its data to a point in the past, these backups are still stored on the device. If your device stops working or you accidentally delete the app, you will lose both the app data and the automatic backups. Not good.
To help that, it is recommended for you to make manual backups whenever you enter new data and email yourself the backup for safekeeping. These backups you can use both for restoring your data on the same device or transfer it to another.
The app allows you to copy its data between iOS devices via email or via iTunes. The easiest way is via email. First you need to create a backup of your data. You do that from the Backups screen, which is accessible via Settings tab on iPhone or under Actions menu (third toolbar button from left) on iPad. Once on Backups screen, you will see several backups already made - these are automatic backups that the app is taking every week or so. It is a good practice to create a manual backup to make sure that all recent changes are included. To do that - tap the Edit button and then the + button that will appear. You will see a new backup now listed at the top. To email this backup, tap it (make sure NOT to tap its icon, that is reserved for transferring data between free and paid versions of the app on the same device) and choose Email as Attachment to send yourself a copy of the data. To restore the data later (or on another device) - open the email on the device where you'd like to restore it and tap the attachment in the email, then follow the steps.