One of the best things I've done on my trip. There were only 4 people in my tour group and the guide was very knowledgeable and adapted to the pace of our group. He told us a lot of interesting things about the plant and animal life as well as some history (there's a look-out point he took us down where they probably saw the planes attack Pearl Harbor). Everything was very prompt. He offered us water and backpacks to use if we wanted and we all got certificates at the end!
I was traveling alone so I didn't want to go off and do a hike on my own when it would be safer to do it with a group. For me it was money well spent. I think it's also good if you're interested in the crater itself and not just the hike up...although you get both on this tour! A great way to spend the morning!
Oh...forgot to mention. Their morning time is perfectly scheduled so that you miss the sunrise rush, but still get to hike up while it's cool. Perfect timing. They really know what they're doing.