I saw this option as well. Even more expensive than Phil. Looks like it allows for infinite adjustability instead of discrete 15* positions. This option leaves the question of which OBB crank to use. I am not particular to what crank it is or what type (1,2,3 speed) as I will only be using 1 chainring position at the 49mm chainline. OBB cranks have fixed spindles, and I would prefer to avoid offsetting the spindle from center and get one that will just 'work'