Legacy solutions transfer the presenter's local screen content to another computer over the Internet. Demodesk on the other hand shares only one browser tab. The screen content of that browser tab is generated on a virtual display in the cloud & synced to all participants at the same time.
Since only one browser tab is shared on the virtual machine in the cloud, the presenter has absolute control over the shared content. Unwanted pop-ups and notifications in the presenter's browser tab are disabled by default.