There are two tours that cover Brussels and you have plenty of time to do both. They cover all the major and some minor spots. Their map also helps to plan where you want to visit.
The audio presentation is pretty good, but you miss some spots because the bus has passed them because the bus has moved past them as you are trying to locate them.
One negative of these audio tours is that there is no one to answer questions about a specific location. The price was right and it was a good value, especially with the Viator discount.
recently during our visit, we full family unertaken the tour. It was good and covered important tourist attractions. Only thing we found is, the attitude of the driver. We dont know the name but he was very rude and that also with children. That is a blackmark because I have always heard and experienced that belgium people are nice. This is my 2nd trip and it was true they are nice except the bus driver attitude towards child.
I love Hop on Hop off and I usually think it is a good way to get familiar with a city but in Brussels it is not worth it. During the week the bus comes every 30 minutes if you are lucky. There is hardly any narration and no announcements what to see at each location. Most stops if you get off it would only take a few moments at the stop and then you would want another bus but then you have to wait 30 min for another one. I rode it to the 1st stop and wanted to switch lines but the 2nd line did not leave for 20min. The last bus left at 4pm but you return from a trip at 4:10 pm so no chance riding the last line. Very badly run!! I even got locked onto the bus at one stop while the driver took a break and did not know I was on the bus.