The Journal has an aspect ratio of 0.647 while the rectangle magnet has an aspect ratio of 0.714 which means that they are not exactly the same shape. That means that an image made for one will not fit perfectly on the other. If you have a white background (typically not as professional looking) then it will probably work just fine. With a colored background you may either get some white showing or part of the image missing. I haven't tested those products so I don't know if CP allows image outside the design specs, generally they do not. If they do then perhaps the "some of the image missing" is an unimportant part and it will look OK. The best thing to do is try it.