So, something on the topic.
So Junkers, like many other brands, is a good and proven brand that belongs to the Bosch group.
I myself also have a Junkers condensing boiler and a Junkers ventilation system.
However, I am not 100% satisfied with the ventilation. Specifically, the bypass flap does not work as I imagine it and as it is handled by other manufacturers. The bypass control is purely designed for energy recovery. Even when it is >30° outside.
Actually, I imagine that the bypass should be closed during the day when temperatures are high in summer operation, and the heat recovery in this case functions as "cooling recovery." At night, when the outside temperature falls below the room temperature, the bypass should be open so that cooler air comes into the house.
With my Junkers, I can only set the bypass to open from temperature X. Where temperature X must be greater than or equal to 15°. In other words, the bypass is open as soon as 15° is reached. At night, okay, but then the bypass is also open during the day at 25, 30, or 35°C.
In practice, the bypass is unusable for me. I will now disconnect it from the system control and control it via my home automation...
So, if the bypass control is important to you, you should inquire about it again before purchasing...