I've fitted them to 2 of my brushes, brilliant! We're getting through the work faster, using less water and are less tired at the end of the day. I've no difficulty using it on 2nd storey flats though one of my workers still hasn't got the knack. if its stiff use the side of the window recess to give you some grip, left side for on, right side for off.
Only problem, I've lost one of the grub screws and after watching the video, probably the spring and the bearing also! ( I think I loosened them too much) So one of them has stopped working properly. Hopefully Gardiners can supply me with spare parts.
That having been said, I would heartily recommend the valve.