I just walked down to the shop and picked up a piece of Koa and a piece of Walnut of about the same size. I would say, based just on feel - I did not weight them, that the Koa is just a little bit lighter than the Walnut.
I've used some Koa to make small boxes, but I have never turned it. I found it very easy to work with.
I've used some Koa to make small boxes, but I have never turned it. I found it very easy to work with.