I booked this trip with good time in advance and I received the confirmation email and the reminder of the tour. However, when I went to the meeting point no one was there. I arrived more or less 10min earlier and I did not see any tour guide. I had a look around the cathedral and no signs of this tour. I waited 15 minutes and nothing. I have been in lots of free tours before but was my first time with this company. I don't recommend.
We were just 3 people, the tour was really nice and the guide was entertaining!