Clipper Tea, which comes in bags without strings.
We've been using this for a while now and it works perfect! You can put loose tea (or a bag without a string) into the egg, add hot water and pull the egg up when your tea is like you want it to be. Because of the glass (borosilicate/pyrex) you can tell how dark it is. But unfortunately because of the glass this teapot is fragile too and needs to be handled with care.
We also got the matching heater which does it's purpose; keeping the tea warm.