The single Harman Kardon CITATION speakers are designed for listening to audio and are not designed for audio in combination with picture. This can lead to synchronization problems when watching videos in some cases.
The CITATION BAR, however, is specially designed for an optimal sound experience in combination with picture.
* Note this mean you cannot cast YouTube video's to your Citation One speaker but you can cast music via the YouTube Music App. It is possible to stream the audio from YouTube video's via Bluetooth. (There also are Mirror Cast and AirPlay 2 options depending on what source you may use).