Won bok, pac choy and gai shoy (mustard cabbages) will all grow well in cool not freezing weather. They will bolt in the heat. I just harvested my first set last week and the next will probably be ready in two to three weeks, I hope.
I grow Hirayama kai choy because it is resistant to white rust and is a local cultivar that is recommended. I have grown the Michili type won bok which is thinnner and taller. I would probably try the win-win variety someday, it sounds good. I do prefer to grow baby bok instead of the bok choy because it is faster and does not form a head. They are also less prone to rot.
Kitazawa seed is a good source for a variety of asian vegetables.
Happy gardening in Hawaii. Gardens are where people grow.