Each 850g can makes approx 10 serves! Depends on strong you'd like the dragonfruit flavour and the cup size you use.
Dragonfruit has a slightly sweet flavour, similar to a cross between a kiwi and a pear. And premium diced dragonfruit is pretty hard to come by.
PS: Jess Lemon developed a recipe with Lychee and Dragonfruit Fruit Tea, if you're interested, check it out here.