Merida City and Shopping Tour

I am looking for some experiences with The Merida City and Shopping Tour from AutoProgresso.

I think we are going to cancel the Uxmal tour we have booked because of some mobility issues. Simply too much walking involved in the hot Mexican sun.

Has anyone taken the Merida City and Shopping Tour? How much walking is involved. I would expect some walking at the Bazaar toward the end of the tour, but how about the rest of it? Is it mostly on the bus with a few stops to get out and explore? Can you hang out on the bus or come back early if you don't want to walk too much? I know quite often when everyone gets off the bus it is parked and locked.

While are are disappointed we won't be able to go to Uxmal, we are looking for something that requires less excursion.