I have not used the tour that you have referenced however, I can say (unless you have trouble walking around ) Florence is also very walk-able and pleasant by foot. So if you are thinking that you need to use a bus tour because everything is spread out...well that isn't true. And you can use a local city bus to get up to and down from Piazzale Micheangelo with no problems (ATAF bus number 13 or 12).
I have used this type of tour for other cities - and if you are on the last leg of your journey and just want to have a fun ride about - then yes this type of tour can be great.
Do you mean the double decker buses?
They are essentially a bus pass valid for 24 or 48 hours to use the bus and you can get on and off unlimited times - in Florence, there are two different routes.
I think they are better in the summer when you can sit above and get good views of the city. You can hear explanations of the city in various pre-recorded languages so it is not a live tour, but it can still be interesting. The routes no longer go right into the center since most of the center is now pedestrian only, so you still need to get off an do some walking to see the main sights.