I pulled the TL numbers from the paper and came up with an STC rating of around 31dB for the 20mm hole model. That is roughly the same STC rating as a decent dual pane window.
As for the air passage, I'm curious about the real world flow numbers.
Just an off the cuff guess: it seems like the core principle is based on resonant cavities which I think would result in higher air pressure in the cavity than inside or outside the window. In a setup like that with calm ambient conditions I wouldn't think much air would actually pass through the panels, the higher pressure in the cavity would act as a bit of a wall. In windy conditions I would imagine much more air would pass through, but I bet there would be a corresponding decrease in sound isolation as air blasting through the cavity wouldn't be able to dissipate as much energy.