it took me less than 5 minutes to cut through a standard u-lock with an angle grinder the first time i did it, which sold me on the heavier u-locks. the extra material is definately buying you time.
another thing to note about that video is that they could position the chain wherever they wanted, which is not always the case in real life and could definately effect the leverage you would get with that cutter.
i've been considering a chain because its more verstile, though. especially when i go back to class, since i'll be able to lock to a lot more things..