Someone might correct me, but I believe it is only in Brazil south that “chimarrão” (how they call this drink) is drank like this, hot and shared.
In Argentina and Uruguay you drink it individually. You can share the recipient with the mate in it, but once you added a refill of hot water and took the first sip, you have to drink it until the end before returning.
And in Paraguay they drink the “tereré” with cold water.
I know you mentioned you don't wanna do ads, which makes sense. But if you're getting 1200 sign ups a day thats worth a lot, and id be happy to chat and see if there's a sponsor opportunity thats uninvasive and that could at least keep you going.
anyhow, you can reach me on Twitter @wagslane or via email: lane @ boot dev.
either way, hope things turn around