Today I had the opportunity to compare my 1990 wild cooked Tuo Cha brewed in a thin gaiwan and in my latest Duan Ni Yixing teapot. The differences were exactly the one I had expected. The Duan Ni gave a more round, mellow and full body brew than with the gaiwan. The gaiwan's brew tasted more thin, with some higher pitched notes and some bitterness on the tongue. It was still very good, as it reflected the quality of this Tuo Cha. But when looking for drinking pleasure, I recommend using the proper teapot to brew it.
To understand and study a tea, the gaiwan gives a more truthful account of its strengths and weaknesses. Also, with a gaibei, it's easier to watch the color of the brew change and decide when best to pour the tea. With the teapot, you have to look at the color of the tea coming out as you start to pour. If the color of the puer is too weak, pour slowly or stop right away.
It was interesting to see how an excellent cooked puer could be further improved with the duan ni teapot. Next time, I will try the same experiment on my younger 2000 cooked pu-er zhuan cha. I expect the improvement to be even more dramatic... (A word of caution to avoid missunderstandings: as bad young puer doesn't turn into gold as it turns old, a duan ni teapot can't change very bad puer into a good one.)