Went on this trip last September and can thoroughly reccomend it.
The first day tour of Phoenix was different, as one wag on board described it as a cross between Monty Python and Benny Hill, it wasn't intended to be. Americans don't do irony very well.
The trips to the National Parks etc were great, though the time spent in Bryce Canyon and Zion Park could have been a bit longer. It's a bit of a culture shock at the end arriving in Vegas after all the natural beauty.
All in all worth going on.