I was going to buy tickets in advance for this bus but after reading all the bad reviews decided we wouldn't use it. However, after a Vatican tour our feet were tired , we noticed a bus at the stop nearbyand so we decided to give it a try.
It was beautiful sunny afternoon and we got the seats at the back of the top level. Maybe we just lucked out but the woman on the bus was very pleasant, when the bus stopped at the starting point for 20 minutes she explained we could wait or if we wanted go to the first 110 bus in the group as it would be leaving in a few minutes. Our feet were still sore, we stayed on- enjoyed people watching and dd another full circuit. The headphones worked just fine for us. Based on our experience, I would recommend it.