Then I want to chime in too: We built last year, moved in December, and none of us had any experience with a [Kontrollierte-Wohnraumlüftung]. Throughout the entire winter, we never felt the need to open a window, really very high comfort and at any time, despite closed windows, a "fresh air feeling." At times, my wife found the humidity too low (~30%), I am still unclear about the connection with the [Kontrollierte-Wohnraumlüftung], it might have nothing to do with it.
Then summer: We have very large window areas on the south side, one underestimates the heating effect these have despite triple glazing. The indoor temperature rose to 25-26 degrees, we overestimated the benefit of the [Kontrollierte-Wohnraumlüftung] (keyword bypass and use of the cool night air). In our case, this only cools by at most 0.6 degrees overnight, your body "heats" against it again. For summer, we have therefore started keeping the shutters down during the day and setting the [Kontrollierte-Wohnraumlüftung] permanently to minimum just to avoid stuffy air. Classic ventilation in the evening is simply more effective for cooling; even with a bypass, the outside air warms up again on its way through the house.
Our personal conclusion: [Kontrollierte-Wohnraumlüftung] is great, we would have it installed again anytime, but rather secondary in summer.