The tumbler is a tea-infuser, as it has a strained top so none of the loose-leafs fall out and you just get the infused water. You can use it for both hot and cold tea drinks. I used it with hot tea and the infuser part worked well. No leaves fell through the top filter! However, when I put the hot tea in the infuser, the glass too was very hot. Sometimes there is some heat-protectant layer so it's not as hot to touch, but I could not hold this very long after I poured the water. I had to wait for everything to cool down before I could drink it, but it was also a good indicator of how hot the water was, so I didn't burn myself when I tried to drink it. So it has some benefits to it as well :P!
In regards to the tea, I have been very pleased with the quality and taste. It is nice to have the variety of teas, because I have not had them in a loose-leaf version before. I was happy!
Overall, I am pleased with this set! Just be careful with the tea infuser because it can be really really hot when you hold it, but that also lets you know it is too hot to drink, so it has some perks.
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*I received this product at a reduced price in exchange for my honest and unbiased review*