Astringent means that the Kakis when they are still hard taste like sloes, which have not got a frost, the mouth we quite unpleasantly dry. When the kakis then ripen (mostly after harvesting), they are soft and no longer astringent from the end of November / beginning of December. They are then also no longer long-lasting if they are soft.
On the other hand, there are also no Kaki varieties with astringent fruits, which means that you can eat them with pleasure when they are still hard. Of course, they can also be softened, but it is not naggy.
After my long year experiences, kakis with a somewhat square and slightly flat fruit shape are not particularly astringent, and kakis with a more rounded geometry are mostly astringent, i.e. only edible after softening!
Concerning growth I am only able to speak accoridng to my Long time experiences in Zone 7b - here both kinds of Kakis are growing similar and hardiness is simlar here also.