This is how it works;
- Between the group and the admins, they take a DIY flavour mix they know to be good.
- The admins (shopowners themselves), buy an absolute heap of the concentrates required to make said mix, acting as a bit of a 'group buy' catalyst
- They then send out the concentrates to the people who have paid for them
- They are much cheaper than buying multiple amount of smaller quantities from even the cheapest online concentrate retailers
- Participants are happy as they are getting cheap concentrates, allowing to make large amount of the flavour at minimal cost
- The shop/admins are happy as they have also bought into the group buy, and sell their juice at retail value for those who don't mix out on the interwebs
They refer the amounts in how much of the final product you can make.
In my case, I paid £23 for 5x50ml concentrate bottles. They would refer to this as 1 litre of juice, even though I'm getting only 250ml.
Hope this helps!