Premium license on Android
Yes, once you have purchased the Premium license, you can use it on multiple devices as long as you are logged in to your Google account, used for the purchase, on all of them.
You can find out how to Restore your Premium license here.
Premium license on iOS
Yes, once you have purchased the Premium license, you can use it on multiple devices as long as you are logged in to your Apple ID, used for the purchase, on all of them.
You can find out more on how to Restore your Premium license here.