I assume that this is like the key keg... I've seen European imports come over in those because you don't need to ship them back. You can serve with CO2 or compressed air because the empty space between the plastic and the bag is what is filled to push the beer out.
This one looks like the same concept but sturdier... I guess the downside is that it's not completely disposable.
Didn't Miller make a big deal about trying this type of thing 20 years ago? I'm probably remembering the time frame wrong but it seems like they came out with a party ball when I was still in Lincoln, NE and that was 18 years back, minimum.
It makes would sense from a handling perspective. Curves and circles are stronger and more resistant to breakage than square corners and straight lines. To make them more appealing I thought the box, that needs to be around the ball, could be made water tight to hold ice. I thought they were a good idea for small parties where 8 gallons was more than was really needed. Of course it was Miller so "good" is relative.