How the Turbopass works
The Turbopass is a digital sightseeing pass. After you buy, it arrives by email, and at the entrance you show the QR code on your phone. You do not need to print anything.
With the Turbopass City you set the number of days. In that time you visit each attraction on the list once, as many as you can manage. With the Turbopass Flex you buy a set number of attractions and pick them from the list. The London Eye is the main difference: with the Turbopass City it costs extra, with the Turbopass Flex it counts like any other attraction.
Turbopass Flex validity
Turbopass itself is not clear on this. The product page says 365 days, while the text on the same page says 30 days. To be safe, count on 30 days and check the information in the shop before you buy.
For some attractions you book a time slot in the Turbopass booking portal after you buy. Do this early, especially in the school holidays.