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To better assist those who might help you, here are the links to the two models you mentioned.

Pure- http://www.trekbikes.com/us/en/bikes...pure_lowstep/#
Shift- http://www.trekbikes.com/us/en/bikes.../shift_1_wsd/#

I haven't had the time to compare the two, but note that basically all of the major brands will have similiar models for any given price point.