There is no central storage of data, data are stored on each monitored system in a database called dbengine, that's all. Cool, right? They do have a data privacy page: https://learn.netdata.cloud/docs/cloud/data-privacy
There is nothing paid, everything is free, both the agent and the cloud app. Do whatever you like with it. There is a pricing policy that will follow sometime in the future but everything that is free today seems that will remain free forever.
If you mean the paid registry thing that they sell, which allows you to keep track of your installations of Netdata on multiple servers, then no.