Would not book through Viator. The voucher says that the concert, brochure, and museum entrance is included. The museum is free to enter and you can buy tickets for the concert at a lower price there. Concert was amazing.
The Vivaldi concert was the highlight of our trip to Venice! Absolutely awesome! We printed our tickets at home and had no trouble using them. We arrived too late to tour the Music Museum, but the staff said the Museum was free and we could come back anytime.