It is certainly frightening if you are not used to heights.
Obviously you get the chance of looking all around the general area. So you get a feeling at least of the neighbourhood and you can understand better the area map.
What I discovered though by going up the top, and by walking with some difficulty around the ring of the Dome, is that I could see through the windows into the interior of the Church.
The Church appeared then quite big and the height (of about 17 metres) even higher than what the actual figure says.