Thank you for reminding me to give an update. Yes we went for it. So it kinda went like this - he comes on site and spends an hour walking around and generally gives a thumbs up for quality of whats been done. He raises a couple of flags on things to check with the architects based on commonly missed standards from his experience. I raise them and got the reassurance they are being done correctly.
Then the real help was mostly psychological. One of the worst months is that final month before the move when there are a thousand tiny mistakes you are catching and the inevitable conflict with the architect. My wife and I used the consultant as a kind of agony aunt to call and ask for advice on how best to approach certain problems. What to fight and what to accept - that kind of strategy. Ultimately cost me about 500 CHF but really felt good to have the support of someone who knew what he was talking about - who was “on our side”.