Crazy, I really cannot see to much utility to having 2 gears so close to each other, most of the time I doubt I would notice much of a difference between 15-16t especially in a freewheel setting. I am guessing it was marketed as a means of not worrying about turning the wheel (flip-flop) to change the ratio...

If they had dual track cogs that had like 15-18 or something, I think I would buy that. It might be nice to change to the easier gear just by moving the chain and adjusting the tension, if need be.