There are two types of license for Tsubook. With a “SUBSCRIPTION” license, you are billed every month and you can access all the paid features on all your devices. With a “LIFETIME” license, you are billed only once and you can access specific paid features on only one device (but it’s possible to transfer the license if you replace or loose your device).
If you purchased the full content before the v3.2 (published in September 2018), the system works differently. More info here