Free Web Access
The people you share your list with do not have to have a premium subscription for basic access to shared tasks using a desktop web browser. When you share a list with someone they will need to create a Todo Cloud basic (free) account and then they will be able to access the list from a desktop web browser.
Synchronization with Devices with Premium Subscription
If someone would like to synchronize tasks from a shared list to their various mobile and desktop devices, they will need to have a premium subscription.