'On average how long would the 50g's take to use?'
It all depends on how often you drink your tea and how strong you like your tea to be. The consumption speed of someone who only drinks two cups a day and prefers weak teas, would be very different from those who drinks 6 cups a day and likes strong teas.
The variation is therefore too big for above question to be generalised. The best way to find out is to order a small package (eg 50g) and use ½ -1 teaspoon of leaves per person depending on the tea type and your preference of the tea strength. Once you have worked out how much you use per day, the answer to the above should be quite clear.
A couple of hints:
1. The amount of tea leaves used per cup/per person is not fixed. Adjust the amount of the leaves to suit your personal preference.
2. The loose leaves can be used repeatedly until the flavour is not more. For example, one lot of green tea leaves can be used for up to 3 infusions and Oolong tea leaves up to 4-5 infusions.