If you leave the hypo on frames/soffits etc for too long it can leave marks.
Never had a problem with it leaving any marks and we have done several hundred over the years
What would you be cautious of applying Hypo to?
One of my customers is a chemist and I have had long discussions with him about this he said providing it is diluted correctly for the item it’s being used on it’s a good multi surface cleaner / steriliser , I have used it on aluminium cladding and it does cause corrosion on raw edges also it does damage the fittings on the hose lines rectus 21 fittings it turned them green and damages the ball bearings in the collar , as I said in another post Ime still learning and different products need to be treated with different strengths start off weak mix and increase in strength
This will probebly be very contraversial but we regularly use it on conservatory roofs with self cleaning glass with excellent results never had a single problem but others have done this with virosol and had major issues: we now regularly use it on conservatory cleans as it will kill green algy in places that you cannot get to with the brush or cloth and the plastic ribs on the roof always look far whiter afterwards