I turned up at 5pm expecting only a few other tourists as it was late in the day. There was actually closer to 50 people waiting. Because of the large number of tourists it was necessary to bring in a second guide and split the groups causing a slight delay.
The guide for my group was Dino. He is a knowledgeable, charismatic, entertaining man with plenty of anecdotes and jokes to tell along the way. His spoken English was excellent.
Sofia isn’t a visually attractive city like Prague or Budapest, so it really needs a guide with a lot of knowledge of the history and culture of the city to keep you occupied and informed as you proceed along the tour.
I found the length of the tour and the pace just right.
I would recommend other Sofia visitors take this tour as the first excursion as it gives a good insight to some of the major attractions in the centre of the city, which you can then go back and visit at your leisure.