I have an old REI Mojave that actually implements a flat and round cord system. I'd say the system works pretty well, except I never seem to remember which is which so I'm stuck in the same boat as two cords of the same =P
Maybe REI owns the intellectual property of a two cord style system? LOL. It is a useful and simple system that should be implemented more.
BTW: Yes the mojave is for women, yes I am male, yes I paid $20 at a gear sale and no I did not own a sleeping bag beforehand.