I know of it, but have never had it. I'm not a fan of kombucha. I don't know how it compares to kvass/gira. I've seen the commercially prepared kvass in various international grocery stores in my area. From the article it sounds like those products are not an accurate reflection of the original product.
"Gira, for all its refreshing qualities, can be a bit of a mischievous drink," Eidukevičius adds. "There's a running joke in Lithuanian households about 'gira explosions' because it ferments in closed containers where enormous pressure can build up like a bottle of Champagne. There's nothing quite like walking into a cellar and finding gira sprayed across the walls and ceiling like some kind of fizzy, rye-bread-scented geyser. It's a testament to how alive this drink is. It's a reminder that we're working with natural processes, and sometimes, those processes have a mind of their own."
Mr wtg's grandparents had this happen to a batch of beer they brewed. Instead of using metal caps, they pounded a cork into each bottle and put the bottles up in the attic to "age" a bit.
Hilarity ensued.