I was initially surprised to see a tumbler of this quality being offered at the 'Big Chain' because it's a bit more sophisticated than the usual plastic ware being touted as tumblers for coffee. People who know tea will tell you hands-down that good tea is best served in Yixing clay servingware because the clay is porous and will eventually retain the flavor of the tea that's repeatedly served in it. Some claim that over time, all you'd need to do to a well-seasoned Yixing cup is to add hot water and you'd have tea without having to add any leaves.
While this tumbler isn't altogether traditional, it is lined with Yixing clay and offers the modern convenience of a plastic outer shell and screw-on lid for traveling. I've used it almost daily for over a month and it hasn't disappointed. Even when I'm home and have the time to steep in a regular ceramic teapot, I still use the tumbler because it usually takes me a while to finish what I prepare (see my bio).
The most interesting feature isn't the fact that it's clay-lined. It is an interactive work of art. When empty or when it's contents are cold, the artwork on the outside features a blue design against a dark navy/purple background. When you pour fresh tea into the tumbler, the clay heats up and the background designs come to life, turning shades of light blue and orange. You always know when your tea is warm.
With Starbucks seeing the light and converting to loose leaf teas this winter, it's nice to see them taking their accessory awareness to a different level as well. The only thing that could improve the tumbler at all is if it included a mesh lid or infuser to brew directly in the tumbler itself, but there are plenty of alternatives out there for the imaginative tea drinker.
If you're looking for a way to bring your favorite tea with you in a briefcase or backpack, this is a great choice.