We've found that these hop-on, hop-off bus services are often a good way to get an initial orientation to a city, and conserve energy for exploring those parts of greatest interest. We had used (and enjoyed) City Sightseeing in Genova a few days before, and so we took advantage of trading in our Genova tickets for a 10% discount in Florence.
But this was a different experience. First, the recorded commentary was the least engaging of any I've experienced for this type of service, being for the most part a long list of "This building was designed by xxxx in the year yyyy," with very little other material to vary the monotony. And the timing of the commentary was frequently out of sync with the bus location.
And, as other reviewers have observed, the drivers and conductors in Florence were often much more interested in talking with each other than paying any attention to passengers. Several times on the upper deck I witnessed passengers trying to disembark at a stop but unable to get down the stairs before the bus started up again.
There's "fatal flaw" in the design of this service, which we saw most clearly in Florence:
1) The buses don't stop at all designated stops (on the Florence Linea A, for instance, they'd frequently drive straight past stops 11, 12, 17, 18, etc. unless someone is waiting there to board);
2) Passengers are adjured not to stand up, both in the commentary and on signs at the seats;
3) There are no bell pulls or bell strips at the great majority of seats;
So, consequently, there's no way short of shouting for most passengers (particularly those at the back of the bus or on the upper deck) to signal that they wish to get off at the next stop.
In my own case, this process -- stand, shout, rapid bus deceleration -- led to a fall, a couple of badly bruised fingers, and a broken watch strap, but it could easily have been more serious. City sightseeing needs to get its act together and install the types of bell cord/strip now provided almost universally in transit buses, or failing that, institute (and enforce) a "stop at every designated stop" policy.