A musical that seemed to be trying hard to shock spectators, and eventually succeeded in doing so, thanks to the intensity of its cast, is being staged at Reduxion Theatre. The 1979 Stephen Sondheim musical “Sweeney Todd: The Demon Barber of Fleet Street,” based on an 1846 “penny dreadful” character who was truly dreadful, was staged with grisly gusto by a 15-member cast. Sweeping onto the stage wearing superb period costumes, the ensemble began by glaring with challenging looks and gestures at ticket holders, as if daring them not to like what was to come. The ensemble’s rendition of the title character’s opening ballad was rousing but hard to follow, telling the back story of Sweeney, who returns from Australia under a new name, bent on revenge for unjust treatment. W.