They've always been very popular in Australia where they are referred to a cordials.
However aren't as concentrated as say MIO (you'd by them in a 2litre bottle) and they do tend to be fairly sugary. And the red (raspberry has the reputation for making kids hyper).
It's definitely one thing I miss now that I'm living in Canada. Mio has the taste from the artificial sweetener and the powders just aren't the same.
Planning on bringing some back on my next trip home.