the instax wide photos are about twice the format of the mini. the mini is meant to be in portrait mode (62mm H and 46mm W), the instax wide has the same hight (62mm) but is 99mm wide. the instax wide camera is quite big. I have both since a year, they are a lot of fun. the mini films are not only half the size, they are also half the price. and the smaller mini camera is easier to take along. so I use it more for fun purpose.
both are quite simple plastic cameras. I would wish a better camera to come, the film is ways better than the old sx70 stuff (the impossible stuff is not really ready yet). and by the way, this was already mentioned: the new polaroid 300 camera is a branded instax mini.