First off, I'll say that this could be a nice place to stay with some improvements. There is ample space with 2 bathrooms, 2 bedroom, and plenty of space to spread out. Steve was prompt in responding to my questions during the stay and they respected our privacy (they have another house where they live behind the one for this listing).
Here are the issues we had and the reason for my low rating; hopefully this will be helpful for prospective guests and for the host to make improvements should they choose:
Cleanliness- at first he place looked fairly clean on the surface. However, inside the refrigerator there were crums and such, kitchen surfaces were sticky feeling, and the couches and other seating smelled like a wet dog.
Bugs - The house has many open windows, which are necessary for air circulation since there's no AC. However there are a number of gaps in the screen mesh which allow bugs in. There was also an issue with the second bedroom where the ceiling tile is starting to disconnect and bugs and worms came through there, especially the night it rained.
Temperature- Air temperature in the house is very dependent on what it's like outside. We were hot the first night since it had been hot and sunny during the day, and the bedroom fans were only so-so. But on the other days it was fine because it was cloudier and cooled off more at night.
Water temp - One thing that needs to be clear in the listed description is that hot water is not guaranteed for showers. Because they use solar energy to heat the water, the days it was cloudy the water was only lukewarm. We would not have chosen to book here had we known that. Personally I would have a backup method for heating water if it were my home.
Distance- The place is located in Hawaiian Paradise Park, which is a huge neighborhood. You could be 15 min from town on the close end, but the property is at the furthest corner from Hilo so it's about 30 min to get to target/safeway. This was a bit further than expected, not a huge deal since we were only there 3 days but would have been annoying for a longer stay.