Whether or not a fisheye is useful depends on what you want to do with it. I have a rectangular Zuiko for my OM2 and find it really useful for surveying buildings as I can cover a room in two frames. I expect to get one when I buy a proper digital camera. With software one can even remove the distortion. Astronomers use the circular image type, I believe. I feel that a stick on front element would be no more than a plaything so it depends whether you are prepared to throw the price away.