On our first full day last week in London, we joined the first BB tour of the day on the "Red" line to get the personal narration - it was our daughter's first trip, and we thought it would be good to get an overview. My husband and I had previously been to London and taken another hop on/hop off tour and our memory is that it covered A LOT more of the sites than this tour and also had a guide. We spent much of our time waiting a stops as there was no traffic early in the morning (surprise) and there evidently are rules about timing for the bus stops as well as how many busses can stop at each site at a time - so we spend a lot of time sitting perfectly still - and at Trafalger Square, got off the bus, went to St. Martin's in the Field, purchased concert tickets for later in the week, and got back on the same bus, which hadn't moved! Once it started moving, we were caught up in terrible traffic, and had we simply gotten off and walked, we would have beaten the bus by 10-15 minutes.
I would not recommend this company.