The tea jar is as ubiquitous in China as the travel mug is in the US. The jar is typically available in polycarbonate, stainless steel, or glass, and includes a sealed cap and a removable filter screen.
The idea is simple. Add tea. Add hot water. Put the screen in place. Cap it. Wait.
When the tea is ready, remove the cap and enjoy. The screen keeps the tea in the jar and away from your mouth. When needed, add more hot water for a second or third infusion. When finished, dump the used leaves and rinse out the jar.
According to that plan, the jars work well and are certainly convenient, easy to hold, and attractive.
Is there a down side? Frankly, yes. At least for some people. The problem occurs because the leaves stay in the tea, and many teas become bitter if infused too long. So, unless a person likes to drink very hot tea very quickly, one’s choice of teas is limited to teas that can stand long infusion times without becoming bitter. This pretty much limits the choices to some Chinese blacks and greens, puerhs, and herbal blends. It pretty much rules out most Indian and Sri Lankan teas. However, since I have by no means tried all possibilities, I welcome feedback on other teas that readers have tried successfully in long infusions.