Paraguayan here. Nice to see a good article talking about Yerba Mate.
A nitpick on Tereré. Tereré is usually the ice-cold version of mate. You drink mate with hot water, tereré with ice-cold water as a refreshment.
The practice of drinking it with fruit juice or some sweet beverage is mostly prevalent on northern Argentina. Here it is mostly viewed as a sacrilege. You drink your yerba mate, whether hot or cold, unsweetened (unless brewed as in cocido; in that case, sweetening it is accepted).
Tereré is something almost essential here in our scorching hot days. What a blessing!
In case you wonder, if you want to get an idea of yerba mate's taste, think green tea. They're not equal, of course, but there's some similarity.