Sorry can't help with info on that route but I did do Blue Hawaii on the weekend and was very disappointed with the route. I was told it was an easy tick for the grade but I didn't expect it to be as easy as it was. I followed the exact line shown in the Arapiles select guide and I think it would be struggling to be 19. I think it is half a grade to a grade easier than other 19's such as Pearls Before Swine and Morphydd, and similar to Tannin but less sustained. There is absolutely no way it is anywhere near 21.
Blue Hawaii is a reasonable route, probably worth one star and probably at the easy end of 19.