We had a great experience. The views are spectacular! Even got to see someone get rescued via Helicopter. They were fine, but it was neat to see how quickly they got to her, and got her to safety. Because of the heat / humidity, the hike was a little more difficult than I thought, but nothing too extreme.
Diamond Head was great but there was no reason we paid extra $$ to sign up for it using this service. We purposely didn't choose a package with transportation because we wanted to arrive early and go at our own pace. We knew it didn't cover the $1 entrance fee pp too. No need for this!! Total waste.