They gave me the wrong start time and then almost left without me so I had to chase them down the street... only to be yelled at in front of the entire bus for being late even though I came out earlier than the time they gave me. The driver had a bit of an attitude about it. The tour itself was ok but not worth the price. This trip was the low point of my trip.
Have done this tour before and had to do it again. The canyon is fantastic. It's only spoilt by the short period of time spent at the viewing point (just 30 minutes). The blow hole stop on the way to the canyon is unimpressive, as are the stops at sights where films have been short. The extended shop at an overpriced tourist retail outlet is particularly unwelcome, but seems to be unavoidable on these sort of trips. However warm it is at sea level, you should take your coat for the canyon viewing deck as it will be cold and windy. You may also find that every photo you take is different due to the constantly changing weather patterns. If you've opted for the river trip and grotto extension, prepare to be underwhelmed by the grotto and to be forced to hula dance on the boat trip back. The view of the final water fall is also unimpressive, but the drivers are happy to transport your luggage on the bus and drop you off at the airport at the end of the tour if this is your last day on the island. The mid-trip meal is at a reasonably priced restaurant ($20ish), but it lasted a little long for my liking and you should be prepared in case you have a comedy driver. If so, you may find that the tour is interactive and that you'll be expected to get involved in the group discussions and hilarity all day long.