I'm not sure why the description stops at 8" tall x 4" wide, or frankly calls them "baby" variety. My Bopaks, if I let them go, have grown to be 18-24" tall and 10-12" wide before bolting. At that stage, the leaves are so enormous that they rival collard greens. I tend to pick off outer leaves and let the choy keep growing, much like lettuces or cabbages. They still taste fabulous and I love to add them to soups, stir fries (the thicker fleshy stems especially are wonderful stir fried soaking up a sauce), pastas, quiches, and pretty much any dish that needs some added braised greens. I do like succession planting some baby varieties alongside this fullsize variety, mostly for aesthetic reasons (baby bok chois are so cute when tossed into ramens or alongside a stir fry!).
One reviewer mentioned something eating the leaves; I have a major problem in my garden with earwigs burrowing into all my brassicas and nibbling on greens, and the Bopaks are no exception. However they seem completely unperturbed by the pest presence and continue to thrive for months. When they bolt (it took until late July this year), I feed them to the chickens earwigs and all, and everybody wins!