Just my opinion of course but I think one can get too caught up in the chase for the perfect tea ware based on clay, firing etc.
Dont get me wrong, I dont mean to suggest that knowing, caring or wanting specific ware is wrong. Only that for the vast majority of people, myself included, we just want good tasting tea.
To that point paying attention to leaf, water, temp and steep time will yeild far more benefit than the tea pot used.
When I look for tea ware I want to know the material is food safe, will it hold heat reasonably well and poor well? Is the pot the right size, how easy is it to clean and does it look good enough I actually want to use it?
Of course everyone has their own criteria and clay type might be one that is important for some. But I wouldn't automatically discredit a pot based on clay...unless it wasn't food safe.
Frankly the average tea drinker, even if they are knowledgable about tea and wares, would be hard pressed to note any difference between clay/firing types without a side by side test of tea and wares. Its just not that important in the whole scheme of a tasty cup of tea.