these options are on SLR cameras, so the image is not upside down, just left to right reversed. For most applications it is very easy to get used to this. However, I find the reversed image can be a bit tricky in situations where the camera has to be tilted up and then pointed to the left or right. It can be tricky to find the right position in terms of converging lines in these cases.
However, the main reason I am looking to buy a prism finder is camera height, particularly for portraits. To have the camera at the height of a human head you could just look directly into a prism, but at that height with a WLF you need to stand on something.