Friendly Streaming Browser: 'Playback' menu items are greyed out

I've downloaded [Friendly Streaming Browser](https://apps.apple.com/au/app/friendly-streaming-browser/id553245401?mt=12) from the App Store, but have not yet paid for 'Streaming Plus'. All of the items in the 'Playback' menu (Jump Forward/Backward and Increase/Decrease Speed etc) are greyed out. Is this a bug, or a feature that is only enabled on paying for the Streaming Plus option? I've emailed the publisher a couple of times, but they have not responded.