I wonder how many kids who eat happy meals at Mc Donalds have a smartphone or similar sized video MP3/MP4 tablet player like the iPod Touch or Amazon Kindle Fire 6 inch tablet.
They show the video from a smartphone's screen which is inserted into the Cardboard VR holder. But, you need to use an app like YouTube with Google Cardboard setting built-in to use these cardboard VR headsets.
Yes, it is sort of like putting your eyes inside of a theater, but the screen is split into two screens to create an image for each eye, and gives the video a 3D appearance.
I think with these cheaper cardboard based VR headsets where you use a smartphone as the display, the user would need to use their imagination more because of the lower resolution screens on most smartphones, and less advance graphics compared to a PC connected to a real VR headset like the Oculus VR headset or Sony VR headset.