Okay, after a quick look, the main differences are that the Pure has 'flat foot/crank forward' technology that allows you to place feet flat on the ground while stopped without getting off the saddle, has more color choices, but only comes in one size. The Shift has a suspension seat post and comes in 3 sizes.

Mechanically, their very similar. Neither will be a speed machine, but depending on your height, the Pure may be a better choice if you have any kind of balance problems while moving at less than a walking speed or stopped.