Shifts absolutely great BUT... as PeeWee Herman said "Everyone has a big but," ... the chain can derail off the Duopar's pulley cage when you roll the bike backwards and bind up the Duopar rear derailleur, leading to BIG problemo if you don't stop rolling the bike backwards. That's why some used to fabricate a pulley cage that captured the chain better on the upper pulley. Your mileage may vary....