The format of the short 1.5 hour tour is enough to get through the highlights. I would however not recommend to book it via this tour operator - MV Dineh Bekeyah Tours.
The cars that all operators use fit 4 persons per row with everybody having a seatbelt. This operator insisted on putting 15 persons on one car so 5 persons per row. The operator also didn't leave us any choice as he added 2 persons after the tour had already started.
This had as a result that couples families and groups did not sit together on the same row to enjoy it together. What is more important - it's against the rules and not safe. I checked during the tour and none of the other operators had more than 4 persons per row.
Another point to note is that the guide did not give any information about the history, geology, evolution etc. of the monument valley. How did the rock formations come to be what is particular about their current state etc. Information was purely limited to the meaning of the monument valley to the native American tribes - something not indicated before I booked the tour.
All-in all it would have been better to just drive the loop by your own car and save the fees. Come to think of it - this is what I would recommend that anyone with their own transport do.