Sorry. Dont have Yahoo Messenger. 

There are a few things that are different between then, but the lens in the 50s is a bit nicer and gives a bit sharper image at the focal point. There was a good comparison site that I read before that I just looked for and couldn’t find again for ya. If you compare them on B&H or something there are minor differences in features, focal length and controls. The ultimate sell for me was that with the 50s you can set the flash to “mountain mode,” whatever that is, and then cover the flash, which effectively allows you to turn it off the flash in low light. Its one of the silly limitations of instax mini that you can’t disable the flash. So thats how I get around it. 

I actually don’t use any expired film unless its just old film of mine that I found and forgot to use. I like the uncontrolled factor to be as contained as possible, which using lomo cameras is pretty high with just the camera, so adding the random effect of expired film feels like too much. So, long story short, I do shoot Kodak Portra 400 and Ilfored 3200, but all fresh. I love the color of the Kodak and I love the texture of the Ilford 3200.