Hiya, Joss.
I work in a teashop part time in Snohomish WA. where we carry these
same tea bottles. I have found from experience that they seem to work
best with a very generous portion of leaf if you are using cold/room
temperature water. If you use boiling/hot water the leaf will tend to
overinfuse pretty quickly, but with priming the leaves for
twenty-thirty minutes the cold/room temperature water will provide a
delicious brew that can be reinfused several times. I personally like
a Bao Zhong (aka Pouchong) type oolong (I know this is kind of
in-between green and oolong, but you have to give it some kind of
label) which I use three teaspoons of leaf at a minimum. I have also
enjoyed larger leaf Darjeelings and Tai Ping Hou Kui greens. Again, I
strongly recommend using cold/room temperature water and letting the
first infusion go for at least twenty minutes before drinking, after
that your leaves are ready to go with fresh water for at least three
more infusions. Also be sure to clean the seals and the bottle well
each day to avoid mildew deposits. Hope this helps you out, happy
quaffing!
Bill