The point isn't whether I think it works in providing mechanical assistance. The point is whether it is intended to provide mechanical assistance, which as you mention from Nike's marketing, seems to be yes.

Try this: http://sportsscientists.com/2017/03/ban-nike-vaporfly-carbon...

By the way, it doesn't really bother me if 3-hour marathoners want to wear them, or even 2:30 marathoners, but if you're competing for prize money, I think this sort of thing should be banned. At least the sport needs a discussion of where to draw the line on such devices.