We had a pleasant stay in Karl's studio. The place is as described, communication with Karl is perfect and all is just fine.
This studio is not your normal Airbnb experience, no other contact than written with the host and seems to be used 100% for rental.
The location is convenient to explore the north coast by car, but Princeville is very weird and unattractive (to me, at least). Next time, I'd rather stay in Kilauea or Hanalei. So despite the fact that the studio itself is good enough (old though), I would not visit again but mainly because of princeville. And if I would choose to stay in Princeville, I would save up a bit longer and get an oceanview.