You will be able to download the CookBook app onto different devices for no extra charge if they are on the same platform (i.e Apple or Android) and if you login to the iOS App Store/Google Play Store using the same app store login.  

You would need to buy the application on both Apple iOS and Android if you have devices on both platforms and if you have different app store accounts on the devices. Please note that as the Apple App Store and Google Play Store are run by different companies, we have no means of sharing the purchase licence between them.

Once you have the app on all devices you can simply login using your CookBook account login details.