By far the most useful tool for exploring the big island on your own (without a tour group). There were so many sights to see and suggested spots that we never would have known about, and it seems to be timed well so that you end up in Hilo by early evening. The narration that explained what you were looking at was great, and we loved the mood music.
Tip: Leave early. We started out from Kona at 9:30. We were done with Hilo by 6, and decided to have dinner there. But that meant driving back to Kona on dark, twisty mountain roads at night. Nerve wracking. If I were to do it again I’d listen to the apps recommendation and start by 8-8:30, finish with Hilo at 5. Pack a picnic dinner or get some kind of take out in Hilo, then continue on to Mauna Kea (which we had to skip.)