The Orbi will block MAC addresses, but that isn't the default.
On the Advanced->Security->Access Control screen, there's are radio buttons for this:
- Allow all new devices to connect
- Block all new devices from connecting
The first option is the most commonly used. When it is selected, any device which has the right passphrase can connect to your network. If you select the second option, you will freeze the list of devices connected to your network. As the wording says, no newcomers will be allowed.
Unless you are both clear on the concepts and paranoid by nature, choose the first option and cross that possibility off your list of potential problems.
