Are you just after the convenience of having a plugin do it?
I haven’t seen how Apple does it, actually.
But I just completed a project presentation with a split screen, showing the presenter on the left and about 70% of the screen on the right showing the slide picture.
But this was reasonably easily achieved just by using the Transform effect to fit each clip into the same view.
Am I missing something?
I can appreciate the convenience of a specialized splitter plugin for many tasks, but not quite seeing it for this one.