Construction costs are currently skyrocketing

Such a ventilation system is clearly for comfort. The purchase costs will never be recovered by the heating costs saved. And if that price is worth it to someone, that's fine. For us, it would have been 12k€ (Thema Baukosten). For that money, a photovoltaic system is now going on the roof.

Insulating the garden shed and 'overwintering' there will probably only be presented as a solution next winter. :’D

or living in the caravan/motorhome while simultaneously lowering the house temperature to 6 degrees (natural refrigerator)

I know we've had this topic many times before. It certainly also depends on the local conditions. Here at Lake Constance there is very rarely normal wind and I have had slamming doors more than once. Of course you can use wedges, but it's annoying. And air exchange is not so good for us because the apartment, firstly, has only 2 exterior walls (but at least one more than the neighbors ;) ) and the windows in the bathroom + storage room are quite small. The topic of costs... two years ago the fans were already included with Town & Country, so I consider price only a limited argument. It is then, of course, not the "all checkboxes ticked" central system with enthalpy exchanger.

Such ventilation clearly serves comfort.

It serves comfort as long as nothing happens.

Yesterday, I was approached by a colleague who knows that we have a controlled residential ventilation system. He has recently been struggling with mold in the bedroom. Due to our working hours, the bedroom is ventilated incorrectly, and this shows on the exterior walls.

He is now trying to ventilate more carefully and is considering retrofitting a decentralized solution as a way out.

This stress and the health cost something?

That is also again the extreme example. If I air out for 10-15 minutes every morning/evening before leaving the house, I have no mold and have never had problems with air exchange in recent years. A controlled residential ventilation system is a nice gadget, but it is not necessary and certainly not as important as some think. Sure, it provides comfort and is nice, but it is definitely not needed. It works perfectly fine without it. And for those who cannot manage to open all the windows daily, I would recommend not installing any stairs in the house at all, since you have to go up and down them several times a day. That just can't be.

That works wonderfully as well. And whoever doesn't manage to open all the windows daily,

Just walk around and look at houses and apartments. The amount of "decorations" and plants on the windowsills is quite astonishing. Maybe also curtains and drapes. Nobody clears all that stuff away several times a day to properly cross-ventilate. Instead, the windows are left tilted – I've seen some nice mold cultures on window sills that were caused by this. In this respect, a ventilation system is more than just "nice to have," because many people simply do not ventilate properly.